Conformal imaging vibrometer using adaptive optics with scene-based wave-front sensing

ABSTRACT

Conformal imaging vibrometer using adaptive optics with scene-based wave front sensing. An extended object is located at the first end of a link, and a reference-free, adaptive optical, conformal imaging vibrometer using scene-based wave front sensing is located at the second end of the link. An aberrated, free space or guided-wave path exists between the ends of the link. The adaptive optical system compensates for path distortions. Using a single interrogation beam, whole-body vibrations of opaque and reflective objects can be probed, as well as transparent and translucent objects, the latter pair employing a Zernike heterodyne interferometer.

FIELD OF THE INVENTION

The present invention relates to vibrometry and to adaptive optics and,more specifically, it relates to a reference-free vibrometer thatfunctions over a turbulent path that utilizes scene-based wave frontsensing of an object to generate the required adaptive optical wavefront correction information to realize diffraction-limited imaging anddiffraction-limited illumination of an object. A compensatedconformal-imaging vibrometer over an extended object can be realizedwith a single probe beam.

BACKGROUND ART

The background art, which is reviewed below, pertains to reference-free,adaptive optics, compensated imaging, scene-based wave front correction,Zernike interferometry and conformal laser Doppler vibrometry. This artmay be of interest to the reader when reviewing this description of thepresent technology.

The basic elements of a typical (prior art) down-link adaptive opticscommunications system 100 are shown in FIG. 1A. The goal of such systemsis to provide real-time compensation for propagation errors, asencountered by optical beams, as they propagate through dynamicdistorting paths, including turbulent atmospheres, optical pointingerrors, imperfect optical elements, multimode optical fibers, etc.

By compensating for optical wave front distortions, one can enhance theperformance of a variety of optical systems. Examples include opticalcommunication systems, remote sensors, precision laser-beam deliverysystems for industrial and medical purposes, and compensated imagingsystems such as in medical applications (ophthalmological imaging andprecision surgical procedures through the eye), microscopy, andcompensated imaging systems. In the latter example, this implies thatone can view complex objects over a distorted path with the same imagequality as if the path were distortion-free. In this case, theperformance of the imaging system can approach that of its theoreticaldiffraction limit, within the so-called isoplanatic volume.

In what follows, first discussed is a generic adaptive optical systemcapable of correcting for path distortions encountered by a so-calleddiffraction-limited reference beam. The reference beam is typically animage-free optical source, whose function is to sample the pathdistortions and, thus, provide this wave front information as input tothe adaptive optical system.

This discussion is followed by a description of a specific adaptiveoptical configuration typical of prior-art, including an example of awave front-error sensing device. This, in turn, is followed by adiscussion of an optical compensated imaging system typical of the art.An understanding of these known art systems will provide perspectivewith regard to the exemplary embodiments of this invention that follow.

As discussed below, compensation of wave front phase errors enables asystem to provide diffraction-limited imaging and viewing of an extendedobject. In general, one first samples and compensates forpropagation-path errors using a diffraction-limited reference beam(e.g., a laser or guide star). Upon compensation of wave front errorsencountered by the reference beam, the optical system can approach itstheoretical diffraction-limited imaging capability of image-bearingbeams that lie within the so-called isoplanatic patch, which is wellknown in the art. As discussed in the exemplary embodiments below, thisinvention enables one to obtain near-diffraction-limited imaging withoutthe need for a reference beam, with application to optical vibrometry.

Turning now to FIG. 1A, the goal of the prior-art system is to enableone to communicate light from an optical source 110 withdiffraction-limited capability through a path distortion. In this case,the optical source is chosen to be of spatial extent less than, or equalto, the diffraction limit of the optical system. Therefore, this sourceis equivalent to a point object with zero image-bearing information,analogous to a single pixel of an image, otherwise known in the art as a“glint.” Light that emerges from this object, which is referredheretofore as a “point-source” or “reference beam,” 120, propagatesthrough space, and, in general, becomes aberrated, as depicted by wavefront 120, as a result of the intervening path distortions or spatialphase errors, such as atmospheric turbulence, labeled by a spatially andtemporally dynamic phase error PHI. It is to be understood that in thepresent invention, PHI is a function of space and time, that is,PHI=PHI(x,t). In essence, the reference beam 120 samples thepropagation-path distortions between it and the optical compensationsystem, 100, including distortions imposed by optical elements withinthe compensation system itself.

At the receiver end of the down-link, a fraction of reference beam 120is collected by telescope 130, which represents the input opticalimaging elements of the adaptive optical receiver system 100. Thecollected light forms an image at the camera, or detector array, 190. Inthe absence of path distortions, the image at the camera plane would bein the form of an Airy disc, since the reference beam 120 is asub-diffraction-limited point source, that is, a single pixel. However,owing to optical propagation phase distortions, PHI, encountered by thereference beam on its path toward the receiver 110, the wave fronts ofthis beam will be aberrated, resulting in a distorted image of an Airydisc pattern at camera 190. As is known in the art, the path distortionsin this scenario can stem from atmospheric turbulence, pointing andtracking errors, imperfect optical elements, thermal and mechanicalperturbations, among other effects. The goal, therefore, of the adaptiveoptical system 100 is to compensate for such path errors so that thewave front of the reference beam at detector 190 can approach thediffraction limit.

Returning to FIG. 1A, the reference beam exiting the telescope (ormicroscope) 130 will be aberrated by virtue of the deleterious pathdistortions, as represented by wave front 140. In this example, theadaptive optical system consists of two optical correction elements. Thefirst corrective element 150 is a so-called tip-tilt compensator, whosefunction is to compensate for overall beam pointing and tracking errors.The second corrective element 160 is a spatial phase modulator, whosefunction is to compensate for fine-scale optical wave front phaseerrors, including focus errors and spatially complex wave front errors.The latter can include static and/or dynamic errors resulting fromatmospheric turbulence, surface and volume refractive-indexirregularities of optical elements. Wave front compensation element 160can be in the form of arrays of continuous and/or discrete optical phaseshifters, such as piezoelectric transducers, electro-optic elements,deformable membranes, MEMS mirrors, liquid crystal cells, photoniccrystals, metasurfaces, among other devices, as is known in the art.

The incident distorted beam 140, first encounters the tip-tilt opticalcomponent 150 followed by the spatial phase modulator 160. The beamsubsequently strikes a beam splitter 165, with one output beam directedto an optical wave front error sensor 170, and with the other outputbeam directed to the camera/detector 190.

The telescope 130 provides an image of the incident beam at the cameraplane 190, and, furthermore, provides an image of the pupil plane at thesurface of the wave front corrective element 160. Hence, the wave frontat the incident aperture is replicated, and, scaled, as needed, at theplane of 160. As is known in the art, the number of phase-controllableelements across the aperture of 160 is determined, in part, by theso-called transverse coherence parameters, otherwise known as the Friedparameters, which is characteristic of the scale size of the turbulentatmosphere.

The spatial bandwidth of the phase modulator 160 is designed toaccommodate the spatial bandwidth indicative of the wave frontdistortions, 120, subject to Nyquist constraints, as is known in theart. In image compensation systems (discussed with respect to FIG. 2Abelow), the spatial bandwidth requirements for the corrective elementare the same, in terms of resolving the wave front error distortionssampled by the reference beam. The imaging resolution, on the otherhand, is dictated by the diffraction limit of the overall opticalsystem. In most cases, the Fried parameter scale size of the turbulenceis far greater than that of the pixel size required to faithfully imagethe object. In other words, the object is comprised of far more pixels(order 10,000 to 1,000,000) than can be described of the distortingmedium (order 100 to 1000).

Each of the compensation elements 150 and 160 is controlled andconfigured in real-time using various classes of optical detectors,algorithms and electronic networks, examples of which are feedback,feed-forward and multi-dither systems, as is known in the art. Oneexample of an optical feedback control loop is depicted in FIG. 1A. Itconsists of a wave front error sensor 170, a processor module 177, and apair of electronic drivers 180 and 185 that provide control signals tothe tip-tilt compensator 150 and the spatial phase modulator 160,respectively. Ideally, the driver 185 will generate a spatial phase mapindicative of a wave front-reversed replica, whose phase is given by-PHI. The resultant beam will therefore possess a wave front that is acombination of the incident phase distortion, +PHI, and the correctionphase map, -PHI, resulting in a wave front with a net phase given asPHI + (-PHI) = 0, indicative of an aberration-free reference beam.

The optical feedback control system is designed to drive the wave fronterror 140 to a minimum. Upon convergence of the servo controlconfiguration, the resultant reference beam that strikes thecamera/detector 190 will be, ideally, free of wave front errors. In thisstate, the overall optical receiver system 100 will provide an image ofthe point-source, reference beam source 110, to its diffraction limit,that is, a planar wave front. Given that this system functions inreal-time, dynamic path distortions can be tracked and compensated, witha residual error determined by the servo-loop gain and its bandwidth, asknown in the art. In general, one can impose temporal modulation ontothe reference glint to realize a down-link communications signal.

It is to be appreciated that, in the down-link system of the prior art,a glint provides the reference. That is, a single-pixel reference isutilized in the prior art. Therefore, it is completely counter to theprior art reference requirements, and is not obvious or anticipated, toreplace the glint (point source) with a whole object, the latterresulting in an effective “image-bearing reference,” to be discussedbelow with respect to FIG. 3A.

To the contrary, in the prior art, much effort is expended to assurethat the reference has zero spatial information; in the prior it is aplane wave (zero spatial information). To deviate from a glint to areference with spatial information, would render the prior art systemuseless.

Turning now to FIG. 1B, a compensated up-link communication system isdepicted in 101. The architecture is identical to that of the down-link,subject to the following differences. One key difference is that aplane-wave laser communications source, 175, is shown, whose function isto direct a laser beam back towards the reference glint location. Thatis, the point-source reference beam and the point-source lasercommunications beam are counter-propagating with respect to each other.The laser is assumed to generate a diffraction-limited output beam,whose wave fronts are planar, 176. That is, this laser source is notencoded with any spatial information. Hence, this laser is ideally, asingle pixel source without any spatial amplitude modulation; that is, auniform intensity source.

In fact, in the existing art, if the return beam is encoded with anyspatial information beyond a plane wave, the system will be rendereduseless, since a diffraction-limited beam will not form at the locationof the glint. Hence, in both the down-link and up-link prior-artsystems, a plane wave is assumed for both ends of the link, in order forthe prior-art systems to function as described.

As will become apparent with respect to this invention, and to bedescribed with respect to the embodiments shown below, the laser can beencoded with spatial amplitude and phase information of an extendedobject, which described in the more recent art, FIG. 3 .

Returning to FIG. 1B, laser beam 176 is directed via beam splitter 177back toward the glint. Note that the feedback servo-system of FIG. 1A isnot affected by the communications laser source 175. Instead, this planewave 176 is encoded via the spatial phase modulator, 160, and tip-tiltcompensator, 150, with an inverted wave front, resulting in a spatialphase, -PHI. This wave front inverted beam is then directed in a reversedirection with respect to the down-link reference back through the sametelescope (or microscope). Upon propagating back through the same pathdistortion as the incident reference beam, a spatial phase shift, -PHI,is encountered by the path distortion, resulting in a net phase error of+PHI + (-PHI)=0. Hence, the up-link beam forms back on the glint as adiffraction limited beam. This reverse-propagating laser can beamplified (amplifier not shown), as is known in the art, resulting in adirected energy beam incident onto the glint location, with applicationto manufacturing and medical applications, among others. Moreover, thelaser, 175, can be temporally modulated to realize an up-linkcommunications signal, forming a simplex or duplex communications link.

In the case of a duplex communications system, the down-link of FIG. 1Aand the up-link of FIG. 1B can occur essentially simultaneously, with atemporal separation less than the time constant of the aberration.Hence, light from the glint 110 (down-link) and light from thecommunications source 175 (up-link) are present at essentially the sametime and are, in fact, counter-propagating with respect to each other.Note that, in general, the phase encoder and tilt compensator can be inthe form of reflective and/or transmission elements, as is known in theart.

Turning now to FIG. 2A, a “compensated image” adaptive optical system200 is shown, typical of the prior art. The goal of this system is toenable precision imaging of an extended object 205 in the presence ofdynamic path distortions 220, with the resultant image viewed by camera290, as viewed through a telescope. The basic adaptive optical aspect ofthe system functions in a manner similar to that of FIG. 1A. However, inthe system depicted in FIG. 2A, there are now two different, distinctinput beams incident upon a telescope, comprised of elements 230 and245. One of the two input beams is designated as a reference beam 210and provides the same function as that of beam 110 of FIG. 1A. That is,it is in the form of a sub-diffraction-limited optical source (e.g., aglint) that samples the path distortions 220. The other incident lightemanating in the region of the reference is an image-bearing beam of anobject, 205, whose spatial information is also distorted by the samepath distortions 220, and whose high-fidelity compensated image issought.

The reference and image-bearing beams both traverse the same inputoptical components and propagation path and co-propagate in the samedirection through space. As is known in the art, both beams are assumedto be within the same isoplanatic volume (or, patch), characteristic ofthe aberration, including the telescope 230, a collimation component,represented by lens 245, tip-tilt compensator 250, spatial lightmodulator 260, imaging optics 247. The reference beam 210 and theimage-bearing beam 205 both impinge upon beam splitter 265.

The beam splitter directs each respective input beam into a differentdirection. The incident reference beam 210 emerges from one port of thebeam splitter as beam 266 and propagates along one direction; and, theincident image-bearing beam 205 emerges from the other port of the beamsplitter as beam 267 and propagates along a second direction. Thereference beam 266 is directed to the adaptive optical control loop, andthe image-bearing beam 267 is directed to a camera/detector module 290.Beam splitter 265 partitions the reference and image beams using avariety of discrimination techniques including polarization, wavelength,spatial frequency, temporal gating, as is known in the art.

In the compensated imaging system 200, the reference beam 266 exitingbeam splitter 265 is directed to an adaptive optical processor in amanner analogous to that described with respect to FIG. 1A. However, inthe compensated imaging system depicted in FIG. 2A, light from theincident reference beam 210 does not strike the camera 290. The solepurpose of the reference beam in this case is to provide path-distortioninformation to the wave front error sensor 270 in the servo-loop sothat, upon correction of the distortions imposed onto the referencebeam, the image-bearing beam can be viewed with little or no distortion.

The feedback loop, operationally, is similar to that of FIG. 1A, namely,the wave front-error sensor (WFS) information output 276 is inputtedinto processor 275. Processor 277 provides error correcting informationto drivers 280 and 285, the outputs of which provide signals to thetip-tilt compensator and the spatial phase modulator, 250 and 260,respectively.

The reference beam 266 emerging from beam splitter 265 passes through anintermediate image plane 255, followed by lens 249, which transforms thebeam to a pupil plane. The beam is then scaled by the telescope (lenses247 and 249) to satisfy the spatial bandwidth constraints of the wavefront-error sensor (WFS) 270. In this system, the WFS is a so-calledShack-Hartmann class of configuration. As is known in the art, theShack-Hartmann WFS consists of a lenslet array 271 and a detector array273, the latter positioned at the focal plane of the lenslets. This pairof elements provides a spatial mapping of the local tilt phase errorsacross the overall pupil-plane aperture, that characterize thepath-distorted incident reference wave front 210.

As known in the art, the required number of lenslets is a function ofthe square of the ratio of the input aperture size to that of thecoherence (Fried) parameter indicative of the incident wave frontdistortions. Under these constraints, it is assumed that the incidentwave front can be described as a series of plane-wave segments, eachwith a different tilt, or phase slope, and all concatenated together.Hence, each plane-wave segment is considered as a diffraction-limitedbeamlet, each with a different tilt angle.

FIGS. 2B (295) and 2C (296), respectively, illustrate the basicprior-art principles of a Shack-Hartmann WFS, as applied to an aberratedwave front 220, and a distortion-free wave front 221 of a plane-wavereference beam. The WFS, identical in both FIGS. 2B and 2C, consists ofa lenslet array 271 and a multi-pixel detector array 273, the latterpositioned at the focal plane of the lenslets.

FIG. 2B (295) depicts the operation of the WFS assuming an inputreference beam whose wave front is aberrated by phase error 220. Eachplane-wave segment of the input beam 222 is incident upon a differentlenslet in the array 271. Since each input segment is planar, albeittilted, a diffraction-limited Airy disc pattern will appear at eachrespective focal plane. However, since each plane-wave segment iscomprised of a tilted wave front, the Airy pattern at each respectivefocal plane at the detector array 273 will be spatially shifted, withthe lateral shift increasing with the slope of the local tilt error. A“beam’s eye view” at the detector surface 273, in the presence of theaberrated beam, is shown in 274.

Note that the array of focused spots does not precisely overlap thegrid-pattern. This is indicative of a typical aberrated beam, whoselocal tilts are randomly distributed. Therefore, each spot at the plane274 has a correspondingly different offset in the (x,y) plane relativeto the grid pattern. As is known in the art, the camera or ccd array 273will require a sufficient number and density of resolvable detectorpixels to measure the offset in spot position to ascertain the localtilt error with sufficient precision.

FIG. 2C (296) depicts the operation of the WFS assuming an inputreference beam whose wave front aberrations have been corrected. In theideal case, the input beam 221 is a perfect plane wave, with acorresponding equiphase surface across the entire input aperture to theWFS. As in FIG. 2B, each resolvable plane-wave segment of the input beam223 is incident upon a different lenslet in the array 271. As before, aset of Airy disc patterns will appear at each respective focal planealong the detector surface 273. However, since each plane-wave segmenthas the same tilt (ideally, zero degrees with respect to the opticalaxis), each respective Airy pattern at the focal plane at the detectorarray 273 will be centered on its respective grid location.

The “beam’s eye view” at the detector surface 273, in the presence ofthe compensated reference beam, is shown in 275. Note that the array offocused spots precisely overlaps the grid-pattern. This is indicative ofan ideal plane wave, whose local tilts are identical. Therefore, eachspot at the plane 275 has a zero spatial offset in the (x,y) planerelative to the grid pattern. It is the goal of the servo-loop adaptiveoptical system to drive an aberrated beam (comprised of a finite numberof tilted plane-wave segments) to a converged wave front whosedifferential tilts approach zero, as in 275.

It is important to emphasize that the WFS detects only the referencebeam, which, by definition, does not contain image information, otherthan the spatial information resulting from the interveningpropagation-path distortions. Hence, based on this prior art, in orderto realize an image-compensation adaptive optics system, only areference beam must be present in the WFS closed loop subsystem. Uponconvergence, a faithful image of the object beam will be detected byvideo camera 290.

However, in many applications, a diffraction-limited reference beam willnot always be present or practical, even in cooperative scenarios(whereby, knowledge of the existence of a reference beam or of anobserver is not a drawback). And, in certain cases, a reference beamoptical source may be undesirable for strategic considerations, sincedetection of a reference optical source by a third party can reveal thepresence and/or location of a covert observer. For these and otherconsiderations, it is desirable to realize a compensated imaging systemwithout the need for a cooperative reference beam.

An embodiment in the more recent prior art of a “reference-freecompensated imaging system” is shown in FIG. 3A. The goal of system 300is similar to that of the prior art in FIG. 2A, namely, to enablehigh-quality imaging of an extended object 305, whose image-bearing beammay have experienced propagation-path distortions along an atmosphericpath 320. However, in this embodiment, there is only a single beam thattraverses the path distortions and received by the image compensationsystem 300 --- the image-bearing beam itself, 306. That is, as opposedto the prior art, there is no independent reference beam (e.g., glint)required to sample the path distortions. In the present case, theimage-bearing beam 306 essentially emulates both the image-bearing beam205 of the prior art, as well as the reference beam 210 of the prior art(both depicted in FIG. 2A).

As depicted in FIG. 3A, the propagation-path distorted, image-bearingbeam 306 is incident upon telescope 330, and subsequently, traverses anoptical collimator represented by lens 345, a tip-tilt compensator 350,a spatial phase modulator 360, imaging optics 347, followed by beamsplitter 365. Beam splitter 365, directs the same image-bearing beaminto two different subsystems. One of the image-bearing beams 366emerging from beam splitter 365 is directed to a spatial filter,followed by a scene-based wave front error sensor (SB-WFS) 370. Theother replica of the image-bearing beam 367 emerging from beam splitter365 is directed to a camera/detector module 390. The spatial filter,which performs low-pass filtering of the pupil plane wave front, iscomprised of transform lens 347, a fixed-diameter diaphragm, 356, andtransform lens 349. The spatial filter is designed to filter out highspatial frequencies beyond the spatial frequency range of theimage-bearing beam to reduce noise in the SB-WFS. The specifications oflens 349 are chosen to provide scaling of the processed pupil-planeimage to match the spatial bandwidth of the SB-WFS, as is known in theart.

The number of resolvable elements of the SB-WFS is chosen to beconsistent with the number of Fried coherence cells within the area ofincident beam to telescope 330/345, which is a function of theatmospheric turbulence conditions along the propagation path, as isknown in the art.

In this embodiment, the SB-WFS determines the local tilt error of thebeam across each subaperture, but, as opposed to performing themeasurement using a reference beam (recall beam 210 in FIG. 2A), thewave front error measurement in the present case is performed using thesame image-bearing beam 306 as that of whose compensated image issought.

In this case, a correlation-based algorithm is used to determine thewave front slope across each subaperture, which is known in the art.This algorithm is necessary, since the wave front across eachsubaperture of the WFS consists of the atmospheric tilt imposed ontoimage-bearing information. This is in contrast to the prior art (recallFIGS. 2B and 2C), in which case the reference-beam wave front acrosseach WFS subaperture is essentially in the form of a tilted planarequiphase surface. In the present case, a more robust mathematicaloperation is necessary to determine the phase slope difference betweennearest neighbor atmospheric-turbulent cells, which include imageinformation.

Returning to FIG. 3A, the adaptive optical servo-control loop of system300 is comprised of the SB-WFS, processor 377, tip-tilt compensator 350and spatial phase modulator 360, the latter pair of which are controlledvia respective drivers 380 and 385, whose respective functions are tominimize residual tip-tilt and spatial wave front errors. This feedbackarchitecture is conceptually similar to that of the prior art (recallFIG. 2A). However, as noted above, the wave front error information isnow derived from measurements of the image-bearing beam, as opposed tothat of the prior art, in which case, the required wave front errorinformation is derived from measurements of the reference beam.

Without loss of generality, in this embodiment, the SB-WFS 370 isconfigured as a Shack-Hartmann system, comprised of a lenslet array 371and a multi-pixel detector 373, the latter of which can be a ccd cameradetector (wherein “ccd” stands for charge coupled device.) We note that,immediately upstream of each respective ccd camera detector is anoptional image intensifier (not shown in the figure), whose function isto provide high-gain, shot-noise-limited image amplification, as needed.The intensifiers can also be gated and synchronized with theimage-sampling rate to enable higher performance compensated imaging,especially, in the case of speckle imaging applications.

As described in FIGS. 3B and 3C below, a corresponding ensemble ofidentical images will appear at the detector plane. Since each lensletmaps a subaperture limited to a single aberration coherence patch acrossthe pupil plane, each of the respective images will be, in general,slightly displaced, laterally, at the detector plane, indicative of thelocal tilt across the respective unit coherence cell. In thisembodiment, a common spatial filter upstream of the lenslet array willrestrict the spectral frequencies of the ensemble of images. The spatialfilter cutoff frequency, determined by the diameter of diaphragm 356, ischosen to enable the SB-WFS to optimally determine the wave front slopeof each respective subaperture image, a tradeoff being the shot-noiselimited performance of the ccd camera detector array on the one hand andthe additive noise induced by the high spatial frequency components ofthe given image on the other hand.

Once the ccd camera detector has acquired the data, it is passed tosoftware, which processes it and estimates the wave-front slopes. Thefirst step in the processing is the correct identification of thelocations of the sub-images formed by the SB-WFS on the ccd cameradetector . Each of these sub-images has a circular field of view. Aninscribed-square sub-image for adequately illuminated subaperture isextracted.

These images are next sent to the slope estimation software. The slopesare estimated in two modes. To estimate the slopes across the apertureat a single instant in time, two references must be known. The firstreference is the default offset location of the sub-images when there isno external aberration in the optical system. These reference slopes aredetermined upon initial calibration of the system. Then a specificsub-image is selected to provide the reference sub-image to which allthe other sub-images are compared. The slopes can also be estimatedthrough time for a single sub-image to enable measurement andcharacterization of the phase aberration through time. In this casereference slopes for all subapertures are not required, and thereference sub-image is simply the first sub-image in the series.

The algorithm that is used to calculate the sub-image shifts functionsby optimally estimating the shift between two images using spatialcorrelation calculations with sub-pixel interpolation. This algorithmhas the advantage that the accuracy and error properties of a scene canbe quickly calculated a priori. To be applied to a small telescope usingthe SB-WFS compensated system, this algorithm has been further enhancedwith added functionality. In particular, formulae were derived whichenable the estimation of the gain of the scene that is used. Thisensures higher-accuracy slope estimates. This gain is calculated byusing a larger portion of the sub-image on the ccd camera detectorextracted from the circular subfield.

Turing now to FIGS. 3B and 3C, respectively, illustrate the basicprinciple of the Scene-Based Shack-Hartmann wave front error sensor,SB-WFS. As opposed to prior-art sensors, in the present case, theincident wave front whose local tilts are to be determined is theimage-bearing beam itself. The respective figures depict the response ofthe SB-WFS in the presence of an aberrated image-bearing wave front 320,and a distortion-free image-bearing wave front 321. The SB-WFS,identical in both FIGS. 3B and 3C, consists of a lenslet array 371 and amulti-pixel detector array 373, the latter positioned at the focal planeof the lenslets.

FIG. 3B depicts the operation of the SB-WFS assuming an inputimage-bearing beam whose wave front is aberrated by 320 and 321,respectively. Each tilted segment of the input beam 322 is incident upona different lenslet in the array 371. Since each segment is replica ofthe incident image 305, a diffraction-limited image will appear at eachrespective focal plane, the diffraction-limit determined by the lensletsubaperture. However, since each respective segment possess an overalltilt, the respective image at the detector array 373 will be spatiallyshifted, with the shift increasing with the slope of the local tilt. A“beam’s eye view” at the detector surface 373, in the presence of theaberrated beam, is shown in 374. Note that the array of image replicasdoes not precisely overlap the grid-pattern. This is indicative of atypical aberrated beam, whose local tilts are randomly distributed.Therefore, each image at the plane 374 has a correspondingly differentoffset in the (x,y) plane relative to the grid pattern. The number anddensity of resolvable pixels of detector array 373 is a function of therequired precision of the tilt measurement, as limited by shot-noiseconsiderations and additive noise, consistent with the upstream spatialfilter response, as is known in the art.

As noted above, each subaperture is designed to collect and image lightfrom a single spatially coherent Fried cell. Hence, a local wave fronttilt error across a given subaperture would result in a slightlydisplaced lenslet image, 374, in a lateral direction, relative to theother subaperture images.

FIG. 3C depicts the operation of the SB-WFS assuming an inputimage-bearing beam whose wave front aberration has been corrected. Inthe ideal case, the input beam 321 is an image-bearing wave, free ofdifferential tilts across the entire input aperture to the SB-WFS. Inthis case, each Fried cell segment will have zero tilt, as depicted bythe segmented set of tilt components, 323. As in FIG. 3B, eachresolvable tilt segment of the input beam 323 is incident upon adifferent lenslet in the array 373. As before, an image will appear ateach respective back plane along the detector surface 373. However,since each image-bearing unit cell has the same tilt (ideally, zerodegrees with respect to the optical axis), each respective image replicaback plane at the detector array 373 will be centered on its respectivegrid location. The “beam’s eye view” at the detector surface 373, in thepresence of the compensated image beam, is shown in 375. Note that thearray of images precisely overlaps the grid-pattern. This is indicativeof an aberration-free image, whose local tilt errors have beencorrected. Therefore, each image replica at the plane 375 has a zerospatial offset in the (x,y) plane relative to the grid pattern.

Returning to the system embodiment of FIG. 3A, a typical video outputsignal of ccd camera detector 373 will appear as an array of nearlyidentical images (albeit laterally shifted by different amounts). Thevideo output of the SB-WFS 370, given by 376, is inputted into the wavefront processor 377, the function of which is to computationallyreconstruct the aberrated wave front errors, as induced by thepropagation path distortions 320 across the entire input aperture to thetelescope 330. The output of processor 377 provides respective tip-tilterror-correction and spatial-wave front error-correction signals todrivers 380 and 385, which, in turn controls the tip-tilt optical andspatial-phase-modulator optical corrector devices, 350 and 360,respectively. Although the optical corrector devices 350 and 360 arerepresented as a transmission-mode devices in FIG. 3A, it is to beunderstood that one or both can be configured as reflective devices, asis known in the art.

An optional narrow bandpass filter 379 is also shown in the optical pathupstream of the SB-WFS and/or imaging camera 390. The function of filter379 is to control and, hence, restrict the optical spectrum to beprocessed and imaged, in the event that out-of-band spectral componentsmay otherwise degrade the signal-to-noise performance of thecompensation system.

In addition, a spatial filter, comprised of lenses 347 and 349 andpinhole 356 is shown, whose function is to control the spatial frequencyspectrum of the distorted image-bearing beam 366 prior to impinging uponthe SB-WFS 370.

The above components constitute the wave front compensation subsystem ofthe overall system 300. Upon convergence of this subsystem, theimage-bearing beam 367 that exits the other port of beam splitter 365will be viewable by camera 390 with minimal wave front distortions. Notethat the resolution of the compensated image at camera 390 can approachthe diffraction limit of the input imaging system and telescope 330/345under ideal conditions.

As is shown below, in the present invention, the SB-WFS performs thefunction of a subsystem of the overall vibrometer system. In thiscontext, this prior art SB-WFS can be viewed as equivalent to adown-link preprocessor. However, the prior art does not consider anup-link and associated details of its encoding, whose function is toserve as a reference beam. Details of an up-link in this context are notanticipated or obvious to one skilled in the art.

Moreover, the prior art does not consider a vibrometer that employs areference-free method to compensate for path distortions encountered bythe image to be probed, which is not obvious to those skilled in the artfor the reasons stated above and in what follows.

The aforementioned state-of-the-art in compensated imaging includes, forexample, (i) U.S. Pat. No. 7,617,060, entitled “Extracting higher orderinformation from scene-based Shack-Hartmann wave-front sensing,” and(ii) U.S. Pat. No. 8,995,787, entitled “Measurement of wave-frontaberration in a small telescope remote imaging system using scene-basedwave-front sensing.”

Another embodiment of the prior art pertains to the field of laservibrometry. A laser Doppler vibrometer (“LDV”) is basically a laserinterferometer designed to remotely sense vibrations of a given objectwithout physical contact of the object, in other words, a non-contactdiagnostic.

LDVs can employ either homodyne or heterodyne detection techniques toascertain the vibrations of the object. In essence, the vibrating objectcan be viewed as Doppler shifting a probe laser beam and the LDV is aninstrument to measure the Doppler spectrum. Vibrometers can be in theform of Michelson, Fabry-Perot, Sagnac, Mach-Zehnder, Fizzeauinterferometers, as is known in the art. LDVs can be configured as bulkdevices, semiconductor lasers, fiber optic lasers and interferometers.Such devices can be utilized in manufacturing, industrial, medical anddefense applications for short or long standoff distance applications.

A common feature of the state-of-the-art in LDVs is that the devices aresingle-mode, point sources. Hence, the vibrations are detected at asingle point along the surface of the object under test. The extensionto multiple-point diagnostics typically involves scanning a single LDVacross the surface of the object with a single LDV or, utilizing asingle line of parallel LDVs in a broom-sweep scan mode.

Another class of multi-point LDV involves surrounding an object with atwo-dimensional or three-dimensional array of parallel LDVs that probethe surface simultaneously so that a so-called conformal imaging laserDoppler vibrometer (“CI-LDV”) can be realized. This class of system hasthe benefit of providing whole-body, multiple vibrational-modecharacterization of an object under test.

However, each object under test requires a specialty fixture,tailor-made to the object, to mount an array (fiber or free-space) ofLDVs that match the shape, configuration, size; and, is thereforelimited to a single given object structure under test.

Moreover, the spatial resolution of the vibrational modal analysis inthe existing art is limited by the number of elements in the array(e.g., the number of fibers). Depending on the size and shape of theobject, the number of sites to be simultaneously examined is limited,due to practical (geometrical) constraints.

Another constraint of the prior art is the standoff distance andline-of-sight between the LDVs and the object, which limits the LDVdensity and number of LDVs in the system.

Yet another limitation of the prior art is that single and multi-pointLDV is limited to distortion-free optical paths between the object andthe LDV. Existing adaptive optical techniques would require referencebeam information for each LDV in an array. Such requirements becomeintractable and impractical for high-density, multi-point objectcharacterization. What is needed is a conformal laser Doppler vibrometercapable of sensing vibrations of an object or group of objects (in aconstellation) without the need of an ensemble of fixed laser (fiber)arrays and mounts that require precision alignment and specialization toservice, in general, objects of different sizes and geometries.Therefore, there is a need to address the foregoing limitations.

Yet another limitation of the prior art is limited to a single-pointvibration measurement with a single beam. What is needed is a means bywhich a single beam can enable the realization of multiple points ofvibration measurement along the surface of a work piece, regardless ofits shape and standoff distance.

Yet another limitation of the prior art is limited to require a secondbeam, such as a point source, guide star or glint located on or near anobject location, by which to enable a probe beam to adapt to dynamicpath distortions. What is needed is a means by which to realize atwo-way communications link between an object located as one end of alink and a laser transceiver (vibrometer) located at the other end ofthe link, without the need for a reference beam.

Yet another limitation of the prior art is limited to require a secondbeam as a reference beam --- such as a beam that illuminates anotherregion of the object (e.g., a plane wave, or via adaptive optics), or asecond beam of a different polarization, or a beam of a time delay ---relative to the first beam. What is needed is a means by which torealize a two-way communications link between an object located as oneend of a link and a laser transceiver (vibrometer) located at the otherend of the link, without the need for a second beam as a reference beam.

Moreover, what is needed is a conformal-imaging laser Doppler vibrometercapable of sensing vibrations of an object or group of objects (in aconstellation) without the need of an ensemble of fixed and finite laser(fiber) array and mounts that requires precision alignment andspecialization to service, in general, objects of different sizes andgeometries. In addition, what is needed is a conformal-imagingvibrometer capable of compensating for path distortions.

Yet another limitation of the prior art is that an additional coherentsource is required to enable a vibrometer to function in the face ofmoving objects and path distortions, using adaptive optical techniques.What is needed is a means by which atmospheric distortions can becompensated using only a single vibrometer beam, without the need of areference laser. Therefore, there is a need to address the foregoinglimitations.

The aforementioned state-of-the-art in laser vibrometry includes, forexample, (i) U.S. Pat. No. 4,833,314, entitled “Variable phase stop foruse in interferometers” (ii) U.S. Pat. No. 8,446,575, entitled “ImagingDoppler velocimeter with downward heterodyning in the optical domain,”(iii) U.S. Pat. No. 7,193,720, entitled “Optical vibration imager,” (iv)U.S. Pat. No. 7,116,426, entitled “Multi-beam heterodyne laser Dopplervibrometers,” (v) U.S. Pat. No. 7,961,362, entitled “Method andapparatus phase correction in a scanned beam imager,” and (vi) U.S. Pat.No. 9,829,374, entitled “Method and system for conformal imagingvibrometry,” (v) U.S. Pat. No. 10,228,277, entitled “System and methodto detect signatures from an underwater object,” (vi) U.S. Pat. No.10,976,239, entitled “Systems and methods for determining polarizationproperties with high temporal bandwidth,” and (vii) U.S. Pat.Application No. 2021/0076944, entitled “System and method fornon-contact ultrasound image reconstruction.”

SUMMARY OF THE INVENTION

The present invention attempts to address the aforementioned limitationsby introducing a conformal imaging vibrometer using reference-freeadaptive optics with SB-WFS to enable remote vibrometry of anystructural geometry which is not amenable with current state-of-the-artlaser vibrometers.

It is an attempt in creating the present invention to provide methodsand apparatus of a reference-free, diffraction-limited opticalvibrometer between a coherently or incoherently illuminated object,located at the first end of an aberrated path and an opticaltransceiver, located at the second end of the path, with an interveningpath distortion. Initially, the received image of the object at thelocation of the laser (vibrometer) transceiver, upon propagation overthe aberrated path, is comprised of distorted object information due topropagation through the distorting medium, such as atmosphericturbulence, a moving body in a manufacturing application, or a medicalenvironment where a moving (e.g., breathing) patient is being evaluated,etc. This embodiment it is believed enables a compensated,distortion-free image of the object to be realized at the opticalcommunications transceiver.

It is a further attempt in creating the present invention to compensatefor the path distortions using only scene-based information, therebyobviating the need for an external, diffraction-limited, coherentreference beam, typical of many adaptive optical systems. In thisembodiment, the compensated image-bearing beam at the transceiver formsan effective reference beam with which to generate the wave frontcorrection information, to spatially encode the communications sourcefor reverse propagation to the object. The result of this process it isbelieved is to realize a distortion-free, diffraction-limited image ofthe object at the second end of the link using the communications sourcelaser.

A further attempt in creating the present invention is to realizediffraction-limited illumination of the object located at the first endof the link by the vibrometer transceiver, the latter located at thesecond end of the link, after reverse propagation through the aberrationpath.

An embodiment of the method utilizes a scene-based wave-front errorsensor (e.g., a Shack-Hartmann or a pyramid sensor) to measure theslopes across of the phase fronts of the distorted object beam, asaberrated over an intervening path, e.g., atmospheric distortions. Theinput to the scene-based wave front error sensor is information from thedistorted image of the object and not of a separate, distorteddiffraction-limited reference beam, typical of conventional adaptiveoptical systems. The scene-based wave-front error sensor results in adistortion-free image of the object and, further, provides wave frontreconstruction information as input to a computational processor, theoutput of which is imposed onto spatial light modulators and tip-tiltcompensators configured in a conventional closed-loop, servo-controlledarchitecture, providing the necessary wave-front correction informationonto a communication laser source. Hence, the present invention does notrequire an external reference beam, as required in conventionalcommunication systems. In the embodiments that follow, the laser sourceis spatially encoded with the spatial-light modulator, enabling adiffraction-limited illumination of the object after reverse propagationover the distorted path. It is an attempt in creating the presentinvention to realize this vibrometer, using only scene-basedinformation, without the need of an external reference.

This invention is counter-intuitive: In conventional compensated imagingsystems, a diffraction-limited reference beam samples the pathdistortions and provides information to compensate for distortionsimposed onto an object beam. In the present invention, the distortionsare sampled by the object beam itself, which provides the necessaryinformation to program (or configure) a plane wave communications laserso that a diffraction-limited communication beam arrives back at thelocation of the object. Hence, the roles of the image-bearing beam andthe vibrometer laser are reversed relative to the existing art, sincethe compensated object beam provides an effective reference to imposeonto the plane wave laser communication source.

To the contrary, one skilled in the art would not consider reversing theroles of an image-bearing beam and laser vibrometer source in such alink. That is, in the present case, the object to be probed providespath-distortion information for the correction of a plane-wave laser,and not vice versa.

One can view this system as programming the wave fronts of a laser withinformation derived from an aberrated object; not the reverse, in whichthe system effectively programs the wave fronts of a distorted objectwith information derived from an aberrated reference beam. Moreover,typically, a coherent laser reference beam is utilized in conventionalcompensated imaging and laser communications systems. In the presentcase, a coherent or incoherent illuminated object beam can be utilizedas a reference to encode the wave fronts of a communications laser.

In another embodiment, the laser source can be modulated with spatialand/or temporal information to be received at the location of theobject. Moreover, this laser beam can be amplified to deliver energyonto the object for medical, industrial, directed energy or otherpurposes. The amplification can be in the form of laser amplifiers,Raman amplifiers or by other means known in the art.

In yet another embodiment, the system can be employed as a whole-bodyconformal imaging Laser Doppler Vibrometer (“CI-LDV”), using coherentillumination, via the laser source, of an object under test, to generatea reference beam comprised of an image of the object. The output of thesystem is in the form of an image of the object, with vibrationinformation of the object superimposed in a one-to-one correspondence.The vibration information can be viewed as a spatial phase (Doppler)modulation imposed onto the illuminated image beam at the location ofthe object, with spatially dependent phase modulation along the surfaceof the object. That is, each resolvable pixel of the compensated imagecan, in principle, provide an independent, modulated signal, indicativeof the vibration of the object at that pixel location.

Thus, a conformal imaging vibration mapping of the object is realizedwithout the need to direct an array of laser beams, say a fiber array,onto the surface area of the object. The system obviates the need fordetailed alignment of each laser vibrometer (as in the prior art), say,in the form of a fiber array, across the surface of the object, but,instead, utilizes the compensated image of the object itself as areference and makes full use of the resolving power of the imagingsystem, as opposed to a finite number of laser vibrometers. Hence, adifferent fixture is not required for a given object’s shape or size.Instead, an image of the object provides the necessary information toprobe the object.

A coherent heterodyne imaging receiver provides spatial vibrationalinformation of the object on a pixel-by-pixel basis, limited by theresolving power of the optical imaging system (e.g., 1000 to 10,000pixels in each dimension, for a ƒ_(#)/10 system across a 10 cmaperture), and, not by the number of independent laser beams or fibersor vibrometers incident upon the object (typically, 10-100 in eachdimension), the latter, indicative of the prior art.

Hence, as an example, this invention provides for the evaluation of thevibrational modes of a high-definition MEMS spatial light modulator, inthis case, which requires only a single beam to illuminate the SLM atsubstantially a normal incidence angle and, thus, to evaluate a 1,000 x1,000 pixel device.

It is a further attempt in creating the present invention to realize areference-free conformal imaging Laser Doppler Vibrometer (“LDV”) of oneor more objects in the field of view of the optical transceiver. Theresultant image will possess vibration information superimposed onto theimage, independent of the shape of the object or the number of objectsin the FOV of the laser transceiver. There is no need to makespecialized fixtures or fiber arrangements or robotic manipulation offiber bundles or free-space multiple beams or beamlets. The presentinvention adapts to any size and/or shape and/or number of objects, solong as it is resolvable by the imaging system.

It is a yet further attempt in creating the present invention to realizea reference-free, compensated conformal-imaging laser Doppler vibrometer(“CI-LDV”) of one or more objects in the field of view of the opticalreceiver without the need for a coherent beam to illuminate the object.Upon illumination by an incoherent beam, the resultant image willpossess vibration information superimposed onto the image, independentof the shape of the object or the number of objects in the FOV of thelaser transceiver. There is no need to manufacture specialized fixturesor fiber arrangements or robotic manipulation of a finite number offiber bundles or free-space multiple beams or beamlets. The presentinvention adapts to any size and/or shape and/or number of objects, solong as it is resolvable by the imaging system, and the resolution ofthe vibrometers is now limited by the diffraction limit of the system(which can number 1,000 to 10,000 pixels in each dimension), rather thanby the number of finite fibers or laser vibrometers (which typically cannumber 10 to 100 elements in each dimension).

It is yet a further attempt in creating the present invention to realizevibrometry of a transparent object, at substantially normal incidence,either via reflection or transmission through the sample. Vibrometerstypically require a probe beam to be scattered or reflected from anopaque or reflective object. In this invention, a Zernike interferometeris utilized to realize a two-dimensional interferogram, modulatedspatially and temporally with vibration information of a whole-bodyobject or a vibrational modes of an extended object or constellation ofobjects. A multi-channel channelizer can be employed for vibrationalanalysis and evaluation.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the disclosure, are only illustrative embodiments of the inventionserve to better understand the principles of the invention inconjunction with this description.

FIG. 1A depicts a prior art typical down-link adaptive opticalcommunications system of the prior art, having the capability ofcompensating for dynamic wave front distortions encountered by anoptical beam upon propagation through an atmospheric path, as viewedthrough a telescope or microscope.

FIG. 1B depicts a prior art typical up-link adaptive opticalcommunications system of the prior art, having the capability ofcompensating for dynamic wave front distortions encountered by anoptical beam upon propagation through an atmospheric path, as viewedthrough a telescope or microscope.

FIG. 2A depicts a prior art typical compensated imaging system of theprior art, having the capability of compensating for propagationdistortions imposed onto an image-bearing optical beam, in the presenceof co-propagating external point-source reference beam that samples thewave front errors along the path, as viewed through a telescope. AShack-Hartmann wave front error sensor measures the phase aberrationsencountered by the propagating beam.

FIG. 2B depicts a prior art Shack-Hartmann wave front-error-sensorsystem, for the case of an incident aberrated reference beam, showing anarray of microlenses that focus the beamlets onto a detector array.

FIG. 2C depicts a prior art Shack-Hartmann wave front-error-sensorsystem, for the case of a compensated (unaberrated) reference beam,showing the beamlets focused onto a detector array.

FIG. 3A shows an embodiment of the prior art, depicting a compensatedimaging system, as viewed through a telescope or microscope, using aShack-Hartmann wave front error sensor, having the capability ofcompensating for propagation distortions imposed onto an image-bearingoptical beam, without the need for a point source reference beam.

FIG. 3B depicts a Shack-Hartmann wave front-error-sensor system used inthe prior art, for the case of an aberrated image-bearing beam, showingan array of microlenses, or lenslets, that focuses the image-bearingbeamlets onto a detector array.

FIG. 3C depicts a Shack-Hartmann wave front-error-sensor system used inthe prior art, for the case of a compensated (unaberrated) image-bearingbeam, showing an array of microlenses that focuses the image-bearingbeamlets onto a detector array.

FIG. 4 shows a flow chart of exemplary embodiments of the presentinvention, an embodiment of which employs a Zernike phase contrastinterferometer. This flow chart also depicts a closed-loop functionalityof the process.

FIG. 5 shows an exemplary detailed embodiment of the present inventiondepicting a reference-free, whole-body, scene-based adaptive opticalconformal imaging vibrometer over an aberrated path (e.g., a turbulentatmospheric path). The vibrometer employs a spatial-dependent coherentheterodyne multi-pixel detector to ascertain a map of vibrational modesof an object or constellation of objects and its evaluation.

FIG. 6 shows an exemplary detailed embodiment of the present inventiondepicting a reference-free, whole-body, scene-based adaptive opticalconformal imaging vibrometer over an aberrated path (e.g., a turbulentatmospheric path) and employing Zernike interferometry, in the case oftransparent, translucent or reflective objects. The vibrometer employs aspatial-dependent coherent heterodyne multi-pixel detector andchannelizer to ascertain a map of vibrational modes of an object orconstellation of objects.

DETAILED DESCRIPTION OF THE INVENTION

The goal of the embodiments described herein is eight-fold: (1)Establish an efficient optical vibrometer between an extended object anda vibrometer; (2) Provide a means to correct for intervening pathdistortions using adaptive optics without the need for a coherent,diffraction-limited single-pixel reference; (3) Provide a means by whichthe whole-body of an object is efficiently illuminated by thetransceiver with only a single beam over the same distorting atmosphere;(4) Provide a means by which a vibrating object can be remotely sensed,and its vibrational modes evaluated, by the system that illuminates theentire object over a distorting path with a single beam; (5) Provide ameans by which a transparent vibrating object can be remotely sensed bythe system that illuminates the entire object over a distorting pathwith a single beam; (6) Provide a means to realize a path-compensated,conformal imaging vibrometer so that a mapping of vibrational modes ofthe an object of arbitrary size and shape can be obtained over anaberrated path (or a moving workpiece or medical patient, etc.) withonly a single coherent or incoherent beam, without the need for afree-space or optical fiber array of individual vibrometers and/orspecialized fixtures; (7) Provide a means by which the spatialresolution of a vibrometer is limited by the diffraction-limited imageof the object and not by a finite number of individual sensingtransducers, fibers or laser vibrometers; and, (8) Provide a means bywhich the process can be repeated (iterated) to realize enhancedsignal-to-noise performance.

In the present invention, the compensated laser vibrometer can be viewedas a communications system, across a distorting atmosphere, with aDoppler-modulated source (e.g., a vibrating object) at one end of thelink and a laser transceiver at the opposing end of the link, asubsystem of which functions as an adaptive optical, scene-based wavefront sensor (SB-WFS) compensated imager.

Turning now to FIG. 4 , a flow chart, 400, is shown that depicts thebasic operation of the system. The basic system 400 is comprised of acommunications link between an object 411 (and 427) and an opticaltransceiver (414, 415, 416, 422, 424 and 425) between which is anaberrated path (413 and 426). The system is comprised of a down-linkpropagation path, 410, and an up-link propagation path, 430, whichiterates (repeats) via path 428, forming a closed-loop network forenhanced performance.

Note that, in practice, the down-link and the up-link paths preciselyoverlap and propagate in opposition to each other. Flow chart 400 showsthem as counter-propagating and parallel, but spatially separated, thelatter for heuristic reasons. It is therefore to be understood thatthese two paths precisely overlap with each other, and that thedown-link and up-link beams (410 and 430) counter-propagate with respectto each other.

Returning to FIG. 4 , an illuminated object, 411, is located at theinitial end of the down-link path, 410, and, as described herein, is thesame object, 427, as at the terminal end of the up-link, 430. Theprocess subsequently repeats via path 428. The object 411 (or 427) canbe in the form of a single object or a group of objects. The objects canbe opaque, reflective, transparent or translucent.

In one embodiment, an object 411 is illuminated by a source, resultingin a field given by E(x,t) = Io(x,t), where Io(x,t) is the spatiallydependent distortion-free illuminated image amplitude. The object 411can be illuminated by either a coherent source, such as a laser, or byan incoherent source, such as an LED array, sunlight, etc. In the caseof an object situated in a long-haul outdoor link, the incoherentillumination can be of the form of sunlight (or a laser). In the case ofa short-range link, in a manufacturing or medical application, theillumination source can be in the form of an LED array (or a laser).

In addition, the down-link illuminated object is modulated by 412,yielding the input down-link modulated signal, M_(D)(x,t). As we discussbelow, the modulation can be externally applied by a separate amplitudeand/or phase and/or polarization modulator or by the vibrating objectitself, the latter of which can be described as a phase modulator, andthe latter system, described as an adaptive optical (or compensated)conformal imaging laser Doppler vibrometer (CI-LDV).

The source can be a single beam; as opposed to the prior art, in whichthe illumination is in the form of a plurality of beamlets, opticalfibers or laser vibrometers, arranged by a specialized fixture toservice a given object’s shape or topology, at a precise standoffdistance. In the present invention, a single beam illuminates theextended object, without the need of precision alignment of fixtures orspecified standoff distances. Moreover, the source can be incoherent(e.g., sunlight, LED arrays) or coherent (e.g., a laser).

Returning to FIG. 4 , light from the illuminated object 411 ---described by the field E(x,t) = Io(x,t), where Io(x,t) is the spatiallyand temporally dependent amplitude of the illuminated image surface ---propagates through a distorting atmosphere 413. The distortion 413 canbe the result of propagation through a turbulent atmosphere, as well asthrough aberrations due to a manufacturing or medical diagnosticenvironment or through an optical fiber. By reciprocity, the pathdistortion is the same for the down-link, 413, as it is for the up-link,426, but in reverse direction. That is, they each impose the samespatially and temporally dependent, dynamic phase error, PHI, onto therespective propagating field in the form E(x,t) = Io(x,t)exp(iPHI),where PHI is indicative of a turbulent atmosphere. Note that PHI, is, ingeneral, spatially and temporally dependent; that is PHI = PHI(x,t).

In either case, light reflected, scattered or transmitted by the objectcan be modulated by a modulation signal, M_(D)(x,t), which can be in theform of an external (amplitude, phase or polarization) modulator, or canbe due to the vibrating object itself or a constellation of independentvibrating objects (excited by either a single acoustic mode or acombination of modal excitations).

The distorted down-link beam is subsequently received by an opticalvibrometer. The vibrometer is comprised of an optical system, 414,typically a telescope or microscope, which also serves to transmit theup-link beam, 425, the latter in reverse sequence. The elements of 414(and 425) can be in the form of transmission and/or reflection optics.

The vibrometer is further comprised of a closed-loop adaptive opticalsystem, 415; a means to generate a compensated image 416 of the object411; a demodulator, that is, a vibrometer (comprised of elements 440,441, 442, 443 and 444); an up-link optical source (a coherent orincoherent source) 421; a local oscillator 420 for coherent detection; ameans by which to spatially encode the up-link source with compensatedimage information 422; and, a means by which to spatially and temporallyencode the up-link source with inverted wave front information 424.

The up-link optical source, 421, typically a laser, is located at theinitial point of the up-link path, 430. The up-link optical beam fromlaser 421 is given by E(x,t) = 1, and is assumed to be adiffraction-limited, plane wave source, possessing plane wave equi-phasesurfaces, with a constant, uniform field amplitude. Hence, the field isrepresented by unity (“1”). This laser beam forms the source of theup-link path, 430. The up-link source can be an incoherent source, suchas a LED array or a coherent source, such as a laser. In the case ofcoherent detection demodulation, the up-link source 421 is a laser,which forms the carrier frequency for the local oscillator 420.

The closed-loop adaptive optical system, 415, is comprised of ascene-based wave front error sensor (SB-WFS), and a wave frontreconstruction processor that imposes wave front correction informationonto the beam via a deformable mirror or other class of spatial phasemodulator, arranged in a servo-controlled, closed-loop architecture, asis known in the art (recall FIG. 3A) This operation results in a beam416, E(x,t) = Io(x,t)exp(-iPHI+iPHI) = Io(x,t), which is that of thecompensated distortion-free, image-bearing beam.

The reconstruction processor 415 utilizes the distorted image of theobject itself as a reference wave front. This is opposed to the priorart, which requires an external, coherent, sub-diffraction-limitedoptical beam such as a laser, glint, guide star, etc. (recall FIGS. 1Aand 1B). As is described in the more recent prior art (recall, FIG. 3A),the wave front processor includes a scene-based wave front sensor(SB-WFS), a computer-based wave front reconstruction subsystem, atip-tilt compensator, a spatial light modulator, and respective drivers.

As a result of the reconstruction wave front processor, 415, an invertedphase, -PHI, is imposed onto the image-bearing down-link 410 receivedbeam 414. The resultant field is given as E(x,t) = Io(x,t)exp(-iPHI+iPHI), thereby resulting in a compensated image of the object416, given by E(x,t) = Io(x,t). Hence, a distortion-free image of theobject is obtained via 416 --- or, via 440, the latter, employingZernike interferometry in the case of a transparent or translucentobject --- thereby completing the down-link.

In addition, as a result of the reconstruction wave front processor,415, an inverted phase, -PHI, is imposed onto the up-link beam source421 via the spatial phase modulator 424 via 415. This results in anup-link beam given by E(x,t) = Io(x,t)exp(-iPHI).

This beam then exits the vibrometer through telescope 425, as up-linkbeam 430. Upon reverse propagation back through the atmosphericdistortion 426, the resultant field is given by E(x,t) =Io(x,t)exp(-iPHI+iPHI) = Io(x,t) at the terminus of the up-link path430, illuminating the location of the object 427 as a distortion-freeimage. Thus, this beam illuminates the object with the same illuminationpattern as the initially illuminated object 411, subject to thediffraction limit and field-of-view (FOV) of the system. At this point,the sequence repeats , via path 428, and the next iteration proceeds,thereby forming a closed-loop, optical communications network betweenobject 411 and the vibrometer.

Returning to FIG. 4 , the down-link communicated signal 412 (i.e., thevibrations of the object) is demodulated by 442 via coherent(heterodyne) detection in the form of a 2-d modulated interferogram,which represents the signal spatially 443, yielding a pixelated mappingof the vibration signal, M_(D)(x,t), 444. In the case of coherentheterodyne or homodyne detection, a local oscillator 420 is present,using the up-link laser 421 as a carrier source. Demodulator 442 iscomprised of a multi-channel heterodyne interferometer, which isdetected by a multi-channel receiver, typically, a high-speed,two-dimensional multi-pixel ccd detector.

For most applications, the measured vibrations are normal to thesurface. In some specific instances, the collected light may not bereceived entirely from the surface normal. In the latter case, thesurface displacement of the vibrating object 411 in the direction normalto the surface can thus be ascertained given the a priori surfacetopology of the object, on a pixel-by-pixel basis, and the resultantoutput of the multi-channel ccd detector, also on a pixel-by-pixelbasis. Using geometrical analysis, the desired normal temporal vibrationamplitude, V_(N), is given by V_(N)(x,t) = M_(D)(x,t)/cos(theta), whereM_(D)(x,t) is the measured spatio-temporal displacement --- i.e., theoutput of the demodulated signal 444 at each resolvable pixel across thesurface of the object --- and theta is the angle between the normal tothe surface and the angle of the measurement displacement (typically,where «1, so, cos(theta) ~1 - ²), which is known by a look-up table,given the shape and topology of the object at each pixel location. Inthis case, the demodulated signal 444 can be viewed as an output from aconformal imaging laser Doppler vibrometers (CI-LDV).

Note, in the present invention, that the number of resolvable vibrationpixels is indicative of the spatial resolution of the object (using asingle-beam vibrometer) and not by the number of fibers or laservibrometers, the latter of which is typical of the prior art in CI-LDVs.Hence, the spatial resolution of the present invention can be in therange of 100 to 1,000 pixels in each dimension, as opposed to the priorart, where the spatial resolution is limited to the number ofindependent vibrometers, fibers, etc. (~1 to 100 pixels in eachdirection).

The system employs two different spatial light modulators 422 (SLM₁) and424 (SLM₂). In the case of SLM₂, inverted wave front information, -PHI,indicative of the path distortion 413, is imposed onto the up-link beam430 by spatial light modulator 424 (SLM₂), via 415. This operationresults in the compensation of atmospheric distortions at the locationof the object 427 at the terminus of the up-link 430.

On the other hand, spatial and temporal amplitude information,indicative of the image-bearing compensated image, Io(x,t), 416 areimposed onto the up-link beam by spatial light modulator 422 (SLM₁).This results in an illumination beam pattern that precisely illuminatesthe object 427 at the terminus of the up-link 430.

It is to be appreciated that there is a fundamental difference in thefunctions of the operations, and, hence, design requirements, of 422(SLM₁) and 424 (SLM₂), vis-à-vis spatial and temporal encodinginformation and image resolution. The function of 422 (SLM₁) is toencode spatial information of the compensated image (Io(x,t)) onto theup-link beam, 421, as derived from 416. Hence, the spatial resolution ofoperation 422 (SLM₁) is that of the extended object, subject to thediffraction limit and the FOV of the system, to resolving the object,416 (and, not the path distortions, 413).

On the other hand, the function of 424 (SLM₂) is to encode wave frontcorrection information (the inverted wave front phase, -PHI) onto theup-link beam to correction for path distortions (due to 413), as derivedfrom 415. Hence, the resolution of operation 424 (SLM₂) is that of thepath distortions (413): the Fried cells, subject to the Nyquistconditions, and not the object information.

Therefore, the functions of these spatial light modulators, and, hence,422 and 424, differ fundamentally (spatially and temporally), which isnot anticipated in the prior art.

As an example, the spatial resolution of a typical atmospheric pathdistortion, and for a typical telescope aperture, is on the order 10 to100 resolution elements in each dimension; whereas the spatialresolution of an object in a typical telescope is on the order of 1,000to 10,000 elements in each dimension, as determined by thediffraction-limited resolution of the telescope and imaging system.

Returning to FIG. 4 , we note that, by reciprocity, elements 415 and 424are one in the same (but in reverse sequence) and are partitioned forease of understanding the function of the overall system. Operation 415receives the down-link, distorted beam, E(x,t) = Io(x,t)exp(+iPHI),whereas operation 424 addresses the up-link light beam, E(x,t) =Io(x,t). The wave front reversed laser up-link beam, E(x,t) =Io(x,t)exp(-iPHI), then passes through the same telescope (ormicroscope) transmitter, 425, as did the down-link beam 413, the latterfor reverse transit through the atmosphere, 426, whose distortion isassumed unchanged during the propagation relative to its initialaberration, 413, as the down-link beam encountered. (This assumption isbased on the round-trip photon transit time from the aberration to thetransceiver and back, being less than the time constant of theaberration, the details of which are well-known in the art.)

After reverse transit through 426, the up-link beam illuminates theobject, 427, with a field given by E(x,t) = Io(x,t) exp (iPHI+iPHI) =Io(x,t), subject to the overall system diffraction limit. Thelight-illuminated object can then become the second iteration of theinitial illuminated object via path 428, and the process repeats asnecessary. Therefore, the illuminated object 427 by the up-link laser421 effectively becomes the down-link illuminated object 411 forsubsequent iterations, thereby increasing the signal-to-noise of thevibrometer.

The following figures describe exemplary embodiments of the system 400,for the case of coherent detection of vibrating opaque objects (FIG. 5), and for the Zernike coherent detection for the case of a vibratingtransparent, translucent or opaque objects (FIG. 6 ).

Turning now to FIG. 5 , details of an exemplary embodiment 500 are shownthat enables a SB-WFS system to realize the following nine functions:(1) illuminate an object 505 with a source 501 or 593; (2) receive animaging-bearing beam 306 from the illuminated object 505, with adown-link modulation signal, 582, M_(D)(x,t) imposed onto the beam by avibrating object; (3) compensate for path distortions between the objectand the vibrometer; (4) generate a compensated image of the object; (5)demodulate the signal via a 2-d heterodyne detector; (6) generate a 2-dpixelated mapping of the vibrations; (7) analyze the vibrational mode(s)of the vibrating object(s); (8) subsequently direct (i.e., transmit) alaser 593 optical beam 584 back to the location of the given object,505, with whole-body illumination capability (limited by the systemFOV), through a turbulent atmosphere 320, with diffraction-limitedperformance; and, (9) subsequently, repeat or iterate the processwhereby the illuminated object forms a closed-loop communicationsnetwork between the object and the vibrometer.

The present invention can therefore be viewed as a path-compensated,reference-free, single-beam conformal-imaging laser Doppler vibrometer(CI-LDV), using scene-based adaptive optics.

In the embodiment shown in FIG. 5 , there is no required referencelaser, guide star, glint or other diffraction-limited reference beamnecessary to sample the path distortions. Instead, an incoherently orcoherently illuminated (501 or 593) image-bearing beam from the objectitself 505 forms an equivalent reference beam 306 that samples theintervening atmosphere, 320.

Note also, as opposed to the prior art (wherein a plurality ofilluminated beams is required of whole-body vibrometry), in the presentinvention, only a single illumination beam is necessary to illuminate anextended object, within the field-of-view (FOV) of the system.

Moreover, as opposed to the single-pixel reference beam of the prior art(recall FIG. 1A), the light emerging from an extended object (i.e., thereference beam) can be comprised of multiple pixels that correspond tothe object itself.

As we discuss below there are two different spatial light modulators,SLMs (360, SLM₂; and 596, SLM₁), that accomplish the respective tasks ofwave front correction (inverted phase = -PHI) and, also, image-bearingreadout [E(x,t) = Io(x,t)].

A scene-based wave front sensor (SB-WFS) system uses this image-bearing(306) inverted wave front wave front information (-PHI) to “pre-distort”and spatially encode the laser beam 584 via SLM₂ 360 and tip-tiltcompensator 350. Specifically, the wave front error sensing (370) andcompensated imaging adaptive optical wave front inversion subsystem(377) are utilized to this end.

Note that the light-based source, can be a coherent source, such as alaser, or an incoherent source, such as an LED array. This embodimentenables one to achieve diffraction-limited communication (vibrometry)with an object without the need of an external point-source referencebeam.

In addition, the compensated image-bearing beam 506 forms the equivalentreference by which to encode an up-link laser 593 via spatial lightmodulator, SLM₁, 596 with compensated image information [E(x,t) =Io(x,t)].

Light (501 or 593) from an incoherently or coherently illuminated object505 propagates as beam 306 through an intervening atmospheric distortion320 and is received by the compensated imaging system, which iscomprised of a telescope formed by optical elements 330, 345 and 547.The telescope elements can be in the form of lenses, mirrors or acombination thereof. Note that the object illumination beam can beexternally illuminated by 501 or can be illuminated by the up-link laser593.

An optional spectral filter 379 is used to remove undesirable spectralbands from adding noise to the system. A polarizer 565 assures that theincident beam 306 and the laser 593 beam 543 are co-polarized forefficient heterodyne detection.

A fraction of the incident beam 306 propagates as 366 through beamsplitter 365, then through a spatial filter, represented by pinhole 556and lenses 547 and 349. The function of this spatial filter is tooptimize the spatial frequency spectrum of the distorted image-bearingbeam 366 prior to impinging upon the SB-WFS 370.

In this embodiment, spatial filter bandpass iris (pinhole) 556 isvariable in diameter, as servo-controlled by 562 via processor 377 tooptimally set the spatial filter bandpass in real-time. Specifically,spatial filter iris 556, is controlled to limit high-spatial-frequencyimage content from “spilling over” into adjacent Shack-Hartmann ccdelements 373, which would otherwise result in a source of noise in theccd array. Using this servo-controller, the fidelity of thereconstructed wave front, as determined by the SB-WFS, will become amore faithful wave-front-reversed representation of the pathdistortions, via this bootstrap modality.

The beam 366 is then incident upon a scene-based wave front sensor(SB-WFS) 370, which, in this case is of the Shack-Hartmann variety (apyramid SB-WFS can also be used), represented by lenslet array 371 anddetector array 373, such as a ccd array. Immediately upstream of the ccddetector is an optional image intensifier (not shown in the figure),whose function is to provide high-gain, shot-noise-limited imageamplification, as needed. The intensifier can also be gated andsynchronized with the image-sampling rate to enable higher performancecompensated imaging, especially, in the case of speckle imagingapplications.

The output 376 of the SB-WFS 370 is processed by 377, which includes awave front reconstruction processor and associated algorithms, as isknown in the art. The output of the processor is directed to a tip-tiltdriver 380 and wave front inversion (phase equal to -PHI) driver 381,which imposes this information onto wave front 306, respectively,comprised of a tip-tilt compensator (otherwise known as a fast steeringmirror) 350 and a wave front spatial phase modulator SLM₂ 360 (typicallya deformable mirror, a MEMS device, a metasurface device, a liquidcrystal spatial phase modulator or equivalent).

The system functions as a servo-controlled adaptive optical processor,which, upon convergence, compensates for wave front distortions 320 andtip-tilt errors, subject to the servo-loop gain, as is known in the art.

Upon closed-loop convergence, the resultant field, E(x,t) = Io(x,t),corresponds to the compensated image-bearing beam 306 from the object505 (subject to the servo-controlled gain, as is known in the art).

Returning to FIG. 5 , a portion of the light 306 is reflected from beamsplitter 365, as beam 367, and is reflected by a second beam splitter591 as beam 506. This distortion-free, image-bearing beam, E(x,t) =Io(x,t), is detected by 590, which is comprised of a video camera (e.g.,a ccd).

The video output 594 from the camera 590 is processed by 592 (e.g.,contrast enhancement, edge detection, etc.). One fraction of the videosignal from 592 --- 572 --- is directed to the video output 599 forviewing, which is a distortion-free image of the illuminated object 505.This image will be compared against the 2-d heterodyne vibration mappedimage 598, as described below.

The other fraction of the video signal, 597, is directed to an amplitude2-d spatial light modulator SLM₁ 596, which encodes the spatialinformation 597 of the compensated image, E(x,t) = Io(x,t), onto laservibrometer source 593 beam 543.

Note that the laser 593 provides a diffraction-limited beam 543 [E(x,t)= 1], which passes through a Faraday isolator 541 to prevent reflectedlight from destabilizing the output of the laser 593. A portion of beam543 passes through beam splitter 540 to the SLM₁ 596.

The spatially modulated light beam 584 propagates through beam splitters574 and 591 and is reflected by beam splitter 365 in a direction counterto the incident image-bearing beam 306.

As described above, beam 584 is subsequently encoded with inverted wavefront correction information (-PHI) by spatial phase modulator, SLM₂,360 and tip-tilt compensation device 350.

Return beam 584 --- now encoded with spatial amplitude information[E(x,t) = Io(x,t)] by SLM₁ 596, and with (inverted wave front) spatialphase information [exp(-iPHI)] by SLM₂ 360 and 350 --- exits thetransceiver through telescope lenses 547, 345 and 330. Thisreverse-propagating beam at the exit of the telescope is given by E(x,t)= Io(x,t)exp(-iPHI).

Returning to FIG. 5 , upon propagation of beam 584 back through theatmospheric distortion 320 (PHI), the resultant beam is given as E(x,t)= Io(x,t)exp(-iPHI+iPHI) = Io(x,t). Hence, the object is illuminated bya diffraction-limited, distortion-free image bearing beam 584substantially similar to the initial illuminated object, Io(x,t). Thefractional (i.e., spatial) illumination across the whole body 505, andthe spatial resolution of the system can be controlled by varying thefield-of-view (FOV) of the of the vibrometer telescope.

The illuminated object 505 by beam 584 forms a subsequent iteration andthe process repeats as beam 306 (via path 428 of FIG. 4 ) for the nextiteration pass of the system, thereby completing a closed-loop networkbetween the object 505 and the vibrometer.

By reciprocity, this counter-propagating laser beam 584 will --- uponreverse propagation through the wave front SLM₂ 360 and the tip-tiltcompensator 350 --- emerge from the system as a wave front-reversedreplica of the incident aberrated beam 306, with image-bearing imageinformation, E(x,t) = Io(x,t)exp(-iPHI). That is, thereverse-propagating light beam will be spatially encoded and emerge in adirection back to the object as wave front-reversed replica of theatmospheric distortions. As the laser beam 584 propagates back throughthe distorting medium (e.g., a turbulent atmosphere), it will “undo” thephase aberrations that were experienced by the initial image-bearingbeam, ultimately, illuminating the original object as adiffraction-limited coherent beam, E(x,t) = Io(x,t).

This reverse-propagating beam will propagate over the same path back tothe initial location of the object 505. Ideally, the return beam willform at the object location as a diffraction-limited beam. Thisinformation will then be directed back to the object, that is, theup-link, as a diffraction-limited beam, minimizing the bit error rate ofthe link.

The process then repeats, with the light-beam illuminated object formingthe required object 505 for a subsequent iteration (recall FIG. 4 ;428), modulation, etc., thereby forming a closed-loop communicationssystem between the object and the vibrometer.

At least two different conditions must be satisfied to assure that thephase-conjugate wave illuminates the object as a diffraction-limit beam.First, it is assumed that the atmospheric path distortion and theposition of the object do not change appreciably during the round-triptransit time of the phase-conjugate beam over the initial path, as isknown in the art. Second, it is assumed that the incident object(down-link) beam 306 and the laser (up-link) beam 584 both fall withinthe isoplanatic volume. The second condition is always satisfied, sincethe incident beam is spatially encoded as an extended object, while thereturn laser beam, in this case, is equivalent to the image of theextended object. Hence, by definition, the return beam will lie withinthe isoplanatic patch, indicative of the atmosphere distortions.

Returning to FIG. 5 , another portion of beam 367 propagates throughbeam splitter 591 and is reflected by beam splitter 574, emerging asbeam 583. This beam is collimated by lens 595 onto detector 578 andforms the terminal end of the down-link (compensated) portion of thesystem. This signal combines with the local oscillator beam 589 torealize pixelated 2-d coherent detection mapping representation of thesignal M_(D)(x,t), as described below.

Returning to FIG. 5 , one fraction of the signal from 592 --- 572 --- isdirected to the video output 599 for viewing. The other fraction, 597,is directed to an amplitude spatial light modulator 596, which encodesthe spatial information 597 of the compensated image onto lasercommunication source 593. The laser 593 provides a diffraction-limitedbeam, E(x,t) = 1, 543, which passes through a Faraday isolator 541 toprevent reflected light from destabilizing the output of the laser 593.

Returning to FIG. 5 , one portion of the laser beam 543 is beam split bysplitter 540 to form the local oscillator beam 589 for heterodynedetection of the down-link modulated signal beam 582, M_(D)(x,t).

The local oscillator beam 589 passes through Faraday isolator 542 toprevent spurious reflections from destabilizing the laser 593. This beamis reflected by mirror 596 and is modulated by modulator 573 (typically,frequency shifted by a Bragg cell, acousto-optic modulator orequivalent, as is known in the art), thereby forming the localoscillator for coherent detection of the beam received from theilluminated object, 583 (the local oscillator beam 589 path isdesignated by the dashed lines).

The frequency-offset local oscillator beam 589 is reflected by mirror597, passes through beam splitter 574 and is collimated by lenses 577and 595, with its output incident upon coherent detector 578.

The signal (due to the vibrating object and/or the down-link signal) isheterodyne detected by the coherent combination of the signal beam 583and the local oscillator beam 589 at detector 578.

Local oscillator beam 589 is designed to have a greater beam diameterthan (image-bearing) signal beam 583 to assure overlap of the localoscillator beam with the signal beam.

The output of detector 578 thereby reveals the coherent detected, 2-dheterodyne demodulated down-link signal 598, M_(D)(x,t,) that wasinitially modulated by the vibrating (and/or wobbling) object,represented by modulation signal 582 --- either whole body vibrations ora multitude of vibrational modes of the body or constellation ofobjects.

A multi-channel channelizer 579 processes the 2-d heterodyne videosignal for analysis, thereby revealing a pixelated mapping of thevibrational modes of the object(s), represented by 598. This mapping canbe compared against the compensated image video signal 599 for furtheranalysis and characterization, the comparison of which can beascertained using image processing algorithms, as is known in the art.

The compensated image of the vibrating object can be viewed spatiallyvia 599, whereas its spatially dependent vibrational spectrum can berevealed by M_(D)(x,t), 589. Note that the system is capable ofproviding spatial information as to the global and/or local vibrationmodes of an extended object (an airplane wing or automotive work piece)or a collection of independent objects (e.g., multi-pixel MEMS devicesfor evaluation). This class of vibrometer illuminates the entire objectwith a single beam (via a telescope or microscope), limited by thediffraction limit of the system and it’s FOV --- which can be on theorder of 1,000 to 10,000 effective pixel locations on the object --- asopposed to the prior art, which requires multiple beams as point sourcesto illuminate multiple points along the surface of an object, limited bygeometrical and structural factors (which is on the order of only 10 to100 interrogation locations on the object) which is much less than thatof the diffraction limit. The entire object is illuminated, which can becontrolled by varying the FOV of the telescope (or microscope).

Note also, that this vibrational information is realized by illuminatingthe entire object within to FOV with a single laser beam, as opposed tothe prior art, which requires multiple, independent beams. Moreover, asopposed to the prior art, the present invention does not require anyphysical fixture attached to the object. Furthermore, the resolution isdiffraction limited; that is, the effective number of interrogatedpixels is limited by diffraction and is not limited by a finite numberof laser vibrometers, as is the case with the prior art. Furthermore,the present invention compensates for path distortions. This is opposedto the prior art, which required a finite ensemble of independent laservibrometers, attached to a fixture at a fixed standoff distance from theobject and, moreover, the prior art system does not compensate for pathdistortions.

It is important to note that the embodiment of FIG. 5 may appearcounter-intuitive to one skilled in the art, upon examination of FIG.2A. This follows, since, in the prior art of compensated imaging systems(e.g., FIG. 2A), a diffraction-limited beam typically, a laser, glint orguide star (recall FIG. 2A, 210), samples the propagation distortionsthrough which an image-bearing beam (205) co-propagates. Thecompensation system senses wave front errors imposed by the atmosphereonto the received coherent reference beam. This information is utilizedto control wave front-compensation elements (e.g., tip-tilt and aspatial phase modulator), so that, upon convergence, the spatialdistortions experienced by the reference beam are corrected, with thereference beam restored to its diffraction limit. Subsequently, animage-bearing beam (which can be illuminated by an incoherent source)co-propagates over the same path as the reference beam, emerging fromthe correction system as a compensated image of high fidelity (limitedby the isoplanatic patch volume, etc.); see 290 of FIG. 5 .

Returning to FIG. 5 , the required reference beam and the coherent laserbeam are both present, but now, with two key (counter-intuitive)differences with respect to the conventional art of FIG. 2A. First, itis seen from FIG. 5 that the image-bearing beam (306) and optical sourcebeam (584) are arranged to propagate in opposition to each another. Thatis, the pair of beams counter-propagates with respect to each other: Onebeam, the image-bearing beam 306, propagates, through the pathdistortions, from the object 505 to the compensation system, otherwiseknown as the down-link (recall 410 from FIG. 4 ). The other beam, 584,propagates from the telescope, upon reverse transit, back to the object,otherwise known as the up-link (recall 430 from FIG. 4 ). Both beamsexperience the same path distortions, but, from opposite directions.

The second key difference of FIG. 5 with respect to the prior art (FIG.2A) is that the effective “roles” of the reference and image-bearingbeams are essentially interchanged with respect to each other, relativeto conventional image compensation systems. In the present embodiment,the effective point-source reference down-link beam of FIG. 2A (210) is,in FIG. 5 , now in the form of the image-bearing down-link beam (306).And the image-bearing down-link beam of FIG. 2A (205) is, in FIG. 5 ,now in the form of an image-bearing up-link beam (584), the formersimply an image to be compensated via the reference beam 205; the latterforming a reference itself, 306. These key differences are not obviousnor are they anticipated by those skilled in the art.

Moreover, the effective image-bearing beam of FIG. 2A is, in FIG. 5 ,now in the form of a diffraction-limited coherent laser beam, 593. Inessence, referring to the down-link portion of the system (recall FIG. 4; 410), the image-bearing beam samples the path distortions, and, usingthe SB-WFS system, the wave front-control elements are configured tocorrect for the wave front distortions that are acquired by theimage-bearing beam (306). The laser beam is then spatially encoded (596)by the compensation system and emerges in a direction directed back tothe initial object, as a wave front reversed replica of the wave frontdistortions that were acquired by the incident, image-bearing beam.

In the prior art, on the other hand, upon convergence of the wave frontcorrection elements, a laser beam (recall FIG. 1B, 175) is injected intothe compensation system. This laser beam (assumed to be in a singlespatial mode and diffraction-limited) is aligned to propagate in adirection counter to the incident image-beaming beam, that is, theup-link.

Returning to FIG. 5 , in the present invention, the laser readout beamsdiffer fundamentally and is not anticipated with respect to the priorart, as shown in FIG. 1B. In the case of the prior art (FIG. 1B), thereference laser is a diffraction-limited plane wave, as shown in FIG.1B, 175. That is, it is of uniform intensity, free of any spatial phaseor amplitude information. In the present case, the communications laseris spatially encoded with the compensated image (599), as encoded byspatial modulator 576, which is counter to what is taught in the priorart.

In the prior art, in fact, by imposing any spatial amplitude informationonto the communications laser of FIG. 1B, 175, the system would notresult in a diffraction-limited beam back at the location of the glintand render the prior art ineffective or useless. Similarly, by notencoding the communications light source with image-bearing information,as in the present invention (FIG. 5 ; 596), the present invention wouldnot result in a diffraction-limited beam 584 that illuminates theextended object, 505.

Returning to FIG. 5 , the reverse-propagating light beam will then format the object location as a diffraction-limited, image-bearing beam.This embodiment can be used to establish a high-performance simplex orduplex communications link between the object and the location of thecompensation system, via a spatio-temporal modulation impressed upon oneof both beams in the system: e.g., temporal modulation of theillumination beam at the object; and/or modulation of the communicationlight source at the location of the compensation device. Light from theobject that propagates back to the compensation system 500 can bedetected, after wave front compensation by elements 350 and 360, usingconventional coherent or incoherent detection techniques for duplexcommunication requirements, as required.

Another class of application can employ a high-energy or ahigh-peak-power laser or laser amplifier chain (593) at the compensatorlocation, which can be used to deliver sufficient optical flux at theobject for materials processing, medical applications or directed energyapplications, etc.

Since the light beam 584 is aligned using the now-compensated image asan effective spatial and angular fiducial marker, it is clear that thelight beam will always reside within the isoplanatic volume, as definedby the path distortions, etc. Hence, the light beam will always bespatially encoded by the system as the intended wave front-reversedreplica.

Note that the illuminated object can be in the form of a single targetor a multitude of targets in space in a directed energy application,such as a group of weld joints in a manufacturing application or kidneystones, cancerous lesions or tooth cavities in a medical application,directed energy for solar panel remote powering, etc. In these cases,the return laser beam, upon reverse transit through the system can beamplified (e.g., Raman amplifiers, fiber amplifiers, etc.) for variousapplications. Other applications follow by those skilled in the art.Moreover, the optical system can be in the form of a space-basedtelescope, a microscope or an optical fiber, dependent upon theapplication design rules.

Vibrometers are well-known in the art. However, in this embodiment, theperformance is enhanced in that the entire object is illuminated by asingle diffraction-limited image-bearing beam, as generated at theremote location of the optical transceiver. Thus, whole-bodyillumination of the object is realized by a single beam, the output ofthe telescope 584. This is opposed to the prior art, which requires aplurality of beams, vibrometers or multiple fibers. The presentinvention has application to enhancing the performance of various remotesensing scenarios, including, as an example, manufacturing real-timeprocess-control sensors, (time-dependent) long standoff distancevibration sensing with application to geo-physical mapping in thepetroleum and defense sectors, target identification by detectingpassive, vibrating target information, medical noncontact diagnostics,and various laser-based ultrasound applications.

Note also, that this vibrational information is realized by illuminatingthe entire object within to FOV with a single laser beam, does notrequire any fixture attached to the object. Moreover, the resolution isdiffraction limited; that is, the effective number of interrogatedpixels is limited by diffraction and is not limited by a finite numberof laser vibrometers, as is the case with the prior art. Furthermore,the present invention compensates for path distortions. This is opposedto the prior art, which required a finite ensemble of independent laservibrometers, attached to a fixture at a fixed standoff distance from theobject and, moreover, the prior art system does not compensate for pathdistortions.

The present invention can be classified as a reference-free,path-compensated, adaptive optical, conformal imaging laser Dopplervibrometer (CI-LDV) using scene-based wave front sensing (SB-WFS).

Turning now to FIG. 6 , details of an exemplary embodiment are shownthat enables the system 600 to function as a path-compensated, conformalimaging adaptive laser Doppler vibrometer, capable of providing temporaland spatial information as to the whole-body or local vibrational modesof an extended object, 605.

Relative to the embodiment of FIG. 5 , the present embodiment providesthe added capability of enabling transparent or translucent objects tobe probed. As such, the object can now be illuminated (601) intransmission or reflection. Moreover, the initial illumination source(601 or 963) can be coherent (e.g., a laser) or incoherent (e.g.,sunlight, LED arrays, etc.). Note that, as opposed to the prior art,only a single illumination beam is required to illuminate extendedobject. Examples of objects to be evaluated include biological samples,plastic objects, thin film structures, semiconductor devices, automotivework pieces, airplane components, or a collection of independentlyvibrating objects, such as multi-pixel MEMS devices, etc.

The basic approach employs Zernike interferometry (Zernikephase-contrast microscopy) as a broadband 2-d phase detection modality,in conjunction with reference-free, scene-based adaptive opticalcompensation of propagation distortions. Given the Zernikeinterferometric approach, in the present case, the object can now beilluminated by an incoherent (in addition to a coherent) source.

This embodiment provides two remote sensing modalities, each without theneed of a coherent reference beam: (1) a path-compensated Zernike imageof the object, e.g., a phase-to-intensity mapping of a transparentobject; and (2) a path-compensated heterodyne 2-d interferogram of thevibrating object.

As described below, path distortions (atmospheric turbulence, etc.) arecompensated by the object beam itself. Hence, the Zernike interferometeroutputs are those of a compensated phase-to-intensity mapped image, freeof path distortions, and without the need of an auxiliary reference beam(e.g., a laser, glint, guide star, etc.).

Recall that this class of vibrometer functions across the entire objectwith a single illumination beam (limited by the FOV of the system), asopposed to the prior art, the latter of which requires a plurality ofbeams as point sources to illuminate multiple points along the surfaceof an object.

As is the case in FIG. 5 , extended regions of an object or a multitudeof objects, each with different acoustic or ultrasound signatures, canbe illuminated by a single beam, the regions of which can be controlledby varying the FOV of the telescope (or microscope). Moreover, thisclass of vibrometer compensates for dynamic atmospheric distortions inlong-haul scenarios as well as short standoff distances typical ofmanufacturing or medical environments (the prior art for extendedobjects and multi-pint interrogation requires a fixed standoff distanceand a plurality of vibrometers, fibers or lasers, and does notcompensate for static or dynamic path distortions).

A flow chart depicting this embodiment is shown in FIG. 4 . The detailsof this embodiment’s flow chart are similar to that described in FIG. 4, with respect to the embodiment of FIG. 5 , with the followingdifferences:

The descriptors in 422, 440 and 441 now refer to Zernike images andZernike interferometry.

In addition, the algebraic field descriptions in the flow chart [E(x,t)and Io(x,t)], are similar to those earlier referenced with respect toFIG. 4 , except now, the functions are typically complex functions,since the object and images can be transparent (or translucent) andhence contain phase factors in general.

Referring to FIGS. 4 and 6 , the output of the Zernike interferometersis detected in two different ways:

In one case, a path-compensated Zernike image of the phase mapcorresponding to the object is obtained, as depicted in the flow chartof FIG. 4 , callout 441 and FIG. 6 , callout 699.

In the other case, a path-compensated, coherently detected heterodyne,2-d spatio-temporal Zernike interferogram of the vibrating object isobtained, as depicted in the flow chart of FIG. 4 , callout 444 and FIG.6 , callout 698.

In the former case, this operation is accomplished using an incoherent(or coherent) illumination beam and direct detection of the transparentobject. Thus, a reference-free adaptive optical compensated Zernikeimage 699 is realized, free of path distortions.

In the latter case, the operation is accomplished using an incoherent(or coherent) illumination beam to realize spatially dependent mappingof a vibrating object via 2-d mapping of the vibrations 698. In the caseof heterodyne detection, the vibrations of the object are equivalent toa 2-d set of phase modulators across the object, which can be viewed asa conformal imaging laser Doppler vibrometer (CI-LDV) withreference-free compensation of path distortions.

In this embodiment, 2-d mapping is realized using a high-speed,high-resolution video detector (e.g., a ccd) 678, with its video outputincident upon a multi-channel analyzer 679, thereby revealing whole-bodyor local vibrations of the transparent object, or constellation ofmultiple transparent objects, 698.

Since the system provides scene-based wave front sensing, the systemprovides for adaptive optical functionality, and path distortions arealso compensated, again, using only the image-bearing beam for wavefront sensing and reconstruction.

Referring back to the flow chart of FIG. 4 , it is assumed that theobject beam 411 traverses a general turbulent atmosphere (413 and 426)between it and the transceiver, 414 and 425. The basic operations of thedown-link 410 and the up-link 430 follow those of FIG. 4 ; recall 410and 430, and the algebraic expressions of the field at each systemfunction.

In the case of a general object (amplitude and phase), it is to beunderstood that the illuminated object field is given as E(x,t) =Io(x,t), where Io(x,t,) is a complex function of x and t. In the case ofa phase-only object (e.g., biological samples, transparent ortranslucent plastic objects), it is to be understood that theilluminated object field is given as E(x,t) = Io(x,t), where Io(x,t,) isa purely imaginary function of x and t.

Turning now to FIG. 6 , details of an exemplary embodiment is shown 600that enables a SB-WFS adaptive optical system, in conjunction with aZernike detector, to receive an imaging-bearing beam, compensate forpath distortions and to provide spatio-temporal information due to astatic (via 699) or vibrating transparent object (698). In either case,an adaptive optical, path-compensated Zernike phase contrast image isobtained for the object 605. In the latter case, a vibration spectrum isprovided, as well as a vibration mapping of the vibrational modes at thesurface of the object, resulting in an effective adaptive optical,path-compensated conformal image laser Doppler vibrometer (CI-LDV),without the need for a finite array of vibrometers. The effective numberof vibrometers in this embodiment is given by the diffraction limit ofthe imaging system, which can exceed a finite number of vibrometer byorders of magnitude along each dimension, the latter, the case of theprior art.

In the system 600 a vibrating object 605 is illuminated by an externalsource (601), which can be a coherent source (e.g., a laser) or anincoherent source (e.g., sunlight, LEDs, etc.) or by the laser in thetransceiver, 693. The spatio-temporal vibrations are represented by aspatial phase modulator 607 driven by a spatio-temporal signal 682[M_(D)(x,t)] across the object as a whole-body vibration or as amultitude of vibrational modes of a transparent object or constellationof transparent objects 605.

The goal is two-fold: (1) to obtain a Zernike image of the object 601;and (2) to obtain a spatial mapping of the vibrations of the object,682, M_(D)(x,t), the latter via Zernike dynamic interferometry.

The beam transmitted or reflected by the object emerges as beam 606,which propagates through the atmospheric phase distortions 320, Themodulated signal image-bearing signal 606 encounters a spatially andtemporally dependent path distortion 320, represented by the phasefactor PHI = PHI(x,t), and is incident upon a vibrometer transceiver,comprised of a telescope (or microscope), represented by lenses 330 and345, and a closed-loop scene-based adaptive optical system, as describedwith reference to FIG. 5 .

Note that these embodiments and specific descriptions are similar tothose of FIG. 5 , except, now, as opposed to imaging of an opaque objectand its vibrational modes, a Zernike image of transparent or opaqueobject(s) and its vibrational modes can be processed, as described inthe flow chart of FIG. 4 and in what follows herein. The system providesa compensated video image of the Zernike image output 699, as well as apixelated vibrational mapping 698 of the modes [signal M_(D)(x,t)] ofthe object 605.

In what follows, we succinctly cover the salient points of thisembodiment. Other details and descriptions are similar to those in FIG.5 .

For heuristic considerations, two Zernike interferometers are shown inFIG. 6 : one to generate the compensated Zernike image (690) of theobject and another to generate the dynamic Zernike interferogram (678).It is to be understood that these two Zernike functions can, inprinciple, be integrated into a single Zernike interferometer usingexisting art optical design rules (subject to differences in thefunctionality of the two interferometers).

Each Zernike interferometer shown in FIG. 6 , is represented by a pairof lenses, with a Zernike plate located at its common focus: The firstZernike interferometer is comprised of lenses 647 and 695, with Zernikephase plate (schematically represented by) 658 at its common focus. Thesecond Zernike interferometer is comprised of lenses 677 and 686, withZernike plate (schematically represented by) 659 at its common focus.

One version of a Zernike plate is comprised is a transparent substrate,with its central region (e.g., a dimple) phase shifted by ¼ of a nominaloptical wave, relative to the substrate, as is known in the art. Hence,as is known in the art, the Zernike interferometer can function in theface of a broadband optical input.

In general, the dimple diameter, d, is typically given by the Airy discdiameter. Note also that Zernike interferometers can also be formedusing annular phase plates as is known in the art. The phase plates inthe figure are therefore representations of a general Zernikeinterferometer for ease of viewing in the figure. In the presentinvention, the “effective” diameter, d, of the phase-shifting region iscontrolled by a servo system (not explicitly shown; as controlled byprocessor 692 and 678) the function of which is to optimize the contrastratio (among other parameters and such parameters as thesignal-to-noise) of the Zernike interferometer output.

Returning to FIG. 6 , spectral filter 379 can be specified to realize anarrow spectral response, as deemed necessary. The spectral response offilter 379 can be controlled by a feedback loop (not shown) with controlparameters determined by processors 377, 692 and 678 to optimize thesignal-to-noise figure of the Zernike output. In addition, a polarizer665 can be placed in the telescope system to define a fixed opticalpolarization in the receiver to maximize the fringe visibility of theZernike output (both for the image 690 and for the 2-d heterodynedetector 698).

The image bearing beam 606 is incident upon beam splitter 365. Thetransmitted beam 366, in turn, is incident upon scene-based WFS 370 andwave front inverted computational reconstructor 377 that drives tip-tiltcompensator (otherwise known as a fast steering mirror) 350 and invertedwave front SLM₂ 360 via respective drivers 380 and 381. This forms aclosed-loop, scene-based adaptive optical subsystem which, uponconvergence, compensates for wavefront distortions 320.

The now-compensated beam 667 reflected by beam splitter 365 issubsequently reflected by beam splitter 591, emerging as beam 608, whichis incident upon Zernike plate 658. The Zernike output beam 608 (formedby lenses 647, 695 and phase plate 658), is collimated by lens 695 andis incident upon video camera 690. The video output 694 of camera 690 isthat of a compensated Zernike interferometric mapping of theimage-bearing phase object(s), 605. The video output 694 is processed by692 (e.g., contrast enhancement, edge detection, etc.) whose videooutput is directed by 672 for viewing of the transparent object in theform of an intensity pattern 699, which is to be compared against theoutput of the Zernike coherent beam output (spatial vibrationalspectrum) 698 to be discussed below. Details of the comparison ofprocessor 679 are typical of image processing algorithms, as is known inthe art.

Another video output of 692, 697, is directed to SLM₁ 696 to spatiallyencode the laser beam 643 with the compensated Zernike spatialinformation, indicative of that of the object 605, emerging as beam 684.(Details of the laser 693, beam 643, Faraday isolator 641, and beamsplitter 640 are similar to corresponding elements of FIG. 5 .)

As is the case with respect to FIG. 5 , in the present case, SLM₁ 696and SLM₂ 360 each perform different functions, each with differentdesign parameters: SLM₁ 696 encodes image-bearing information (in theform of a Zernike output 697) onto the reverse transit beam 684, whosespatial resolution matches that of the object 605, subject to Nyquistconditions (on the order of 1,000 to 10,000 pixels along eachdimension).

On the other hand, SLM₂ 360 encodes inverted wave front information(-PHI) onto beam 684, whose spatial resolution matches that of thepropagation distortion 320 (on the order of 10 to 100 pixels in eachdimension, subject to the Nyquist conditions).

Returning to FIG. 6 , upon encoding beam 643 with SLM₁ 696, beam 684 isdirected into a reverse direction relative to beam 667 for reversetransit through the inverted wave front encoding SLM₂ 360 and tip-tiltcompensator 350.

The beam 684 emerging from the vibrometer [E(x,t,) = Io(x,t)exp(-iPHI)]then propagates in a counter-propagating direction with respect to theinitial image bearing beam 606, then, through the path distortion 320[exp(+iPHI)], emerging as a compensated wave front image-bearing beam684 [E(x,t,) = Io(x,t)], which is then incident upon object 605 therebyilluminating the object with a diffraction-limited image. The sequencesubsequently repeats for a following iteration through the system, viapath 428 (recall, FIG. 4 ).

Returning to FIG. 6 , a fraction of the compensated image-bearing beam667 reflects from beam splitter 574 as beam 683, which is incident upona second Zernike interferometer, comprised of phase plate 659, boundedby lenses 647 and 686. The output of this second Zernike is collimatedand is incident upon a high-resolution, high-speed, large-area 2-d videocamera (e.g., a high-speed ccd) 678. The output of this second Zernikeinterferometer from lens 686 is incident upon a large-area video camera(e.g., a high-speed ccd) 678.

Also, incident upon camera 678 is a local oscillator beam 689 (shown asdashed lines in FIG. 6 ). The local oscillator is similar to thatdescribed in FIG. 5 , and, in this case, 673 (in the form of a Bragggrating, acousto-optical modulator or equivalent) generates thefrequency offset for the local oscillator beam 689. Recall that laser693 beam 643 propagates through Faraday isolator 641 and reflects offbeam splitter 640 as beam 689. The Faraday isolators prevent spuriousreflections from destabilizing the laser 693. The local oscillator beam689 (dashed lines) is then incident upon a Zernike interferometer,formed by lenses 677 and 686 with Zernike phase plate, represented by659 (Note that local oscillator beam 689 can also be coupled ontodetector 678 using beam splitters downstream of lens 686, as deemednecessary.) The beam waist of the local oscillator beam 689 is greaterthan that of signal beam 683 to assure overlap of the signal beam acrossthe entire coherent detector active area of 678.

This output 698 corresponds to a high-speed interferogram of the spatialvibrational modes of the object, which can be superimposed on acompensated image 699 for comparative reasons of the illuminated object605 and modulation information 682.

A multi-channel processor 679 yields the surface vibrations,accelerations or displacements from the illuminated object 605 at eachspatially resolvable location, within the FOV of the telescope systemlenses 330, 345 and 347. The resultant data can be compared to thecompensated image 699 for a detailed mapping analysis. Conventionalimage processing algorithms can also be implemented for this operation,as is known in the art. The pixelated mapping of the vibrational modesis given by signal 698 M_(D)(x,t). This system is equivalent to anadaptive optical, reference-free, compensated, conformal-imaging laserDoppler vibrometer (CI-LDV) using a scene-based WFS.

As opposed to the prior art, the path distortions are compensated, theobject can be illuminated by a single (coherent or incoherent) beam,independent of standoff distances and the vibrations are revealed atpixel locations determined by the number of diffraction-limited pixelsacross the surface and not by a finite number of laser vibrometers (andassociated fixtures), the latter constraint of which is in the priorart.

The foregoing description of the invention has been presented forpurposes of illustration and description and is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching. The embodiments disclosed were meant only to explain theprinciples of the invention and its practical application to therebyenable others skilled in the art to best use the invention in variousembodiments and with various modifications suited to the particular usecontemplated.

As an example, the system can be used to service other portions of thespectrum, from the ultraviolet to the infrared to mm wave and below,with application to radars, hyperspectral imaging, among others.Dual-conjugate optical systems can be implemented to simultaneouslycorrect for near-field aberrations (e.g., turbulent boundary layers) andfar-field aberrations (e.g., distributed atmospheric turbulence).Moreover, different classes of wave front-error sensors can be used inplace of the Shack-Hartmann WFS, such as a pyramid WFS. Furthermore,acoustic analogs of this system can be realized, with application tomedical and nondestructive evaluation of materials, among others.

It is to be appreciated that the compensated optical imaging system canbe implemented to service a variety of imaging-based applications beyondatmospheric viewing systems. Hence, when the basic imaging system isreferred to as a telescope, it is to be understood that the presentteachings and embodiments can also be applied, without loss ofgenerality, to compensated microscopy systems, speckle imaging,ophthalmological systems, communications systems, and the distortionpath is referred to as a dynamic atmosphere, ultrasound imaging systemsand so on. Moreover, optical reflective as well as optical transmissiveelements can be implemented in the above-mentioned embodiments.

Similarly, when the distortion path that imposed the wave frontdistortions to be compensated is referred to as a dynamic atmosphere, itis to be understood that the teachings can also be applied, without lossof generality, to a correct for propagation-path distortions such asthose experienced by imperfect optical elements, and static and/ordynamic distortions due to propagation through, or scattered from,ocular systems, skin tissue, clouds, turbid liquids, industrialenvironments, and so on. The scene-based (Shack-Hartmann) wave-frontsensor could also be used in a post-processing scheme such asdeconvolution or to augment speckle imaging.

It is also understood that the teachings herein can apply to guided-waveimplementations of the present invention, given the state-of-the-art inoptical fiber devices including, but not limited to, modulators, Faradayrotators and isolators, polarizers, sensors, fiber couplers andsplitters, photonic crystal fibers, holey fibers, diode-pumped fiberlasers, amplifiers, Raman fiber amplifiers and MEMS devices. Fiberrealizations can also be employed in place of bulk optical elements.

Furthermore, it is also to be understood that the teachings describedherein can also enable reference-free compensated imaging and beamdelivery for systems that operate in other regions of theelectro-magnetic spectrum. As an example, precision compensated imagingover propagation-path distortions in the THz regime can be realized byemploying appropriate THz detectors, sources, and beam formingcomponents (THz sensors, imagers, diffraction gratings, photoniccrystals, modulators, etc.) analogous to those in the opticalembodiments. In addition, it is to be appreciated that the extension ofthe techniques taught herein can also apply to acoustic and ultrasonicreference-free imaging and beam forming systems through acoustic-baseddistortion paths.

The possibility of modifications and variations will be apparent topractitioners skilled in the art. No limitation is intended by thedescription of exemplary embodiments which may have included tolerances,feature dimensions, specific operating conditions, engineeringspecifications, or the like, and which may vary between implementationsor with changes to the state of the art, and no limitation should beimplied therefrom. Applicant has made this disclosure with respect tothe current state of the art, but also contemplates advancements andthat adaptations in the future may take into consideration of thoseadvancements, namely in accordance with the then current state of theart. It is intended that the scope of the invention be defined by theClaims as written and equivalents as applicable. Reference to a claimelement in the singular is not intended to mean “one and only one”unless explicitly so stated. Moreover, no element, component, nor methodor process step in this disclosure is intended to be dedicated to thepublic regardless of whether the element, component, or step isexplicitly recited in the Claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. Section 112, as it exists onthe date of filing hereof, unless the element is expressly recited usingthe phrase “means for ... ” and no method or process step herein is tobe construed under those provisions unless the step, or steps, areexpressly recited using the phrase “comprising the step(s) of .... ”

The foregoing Detailed Description of exemplary and preferredembodiments is presented for purposes of illustration and disclosure inaccordance with the requirements of the law. It is not intended to beexhaustive nor to limit the invention to the precise form(s) described,but only to enable others skilled in the art to understand how theinvention may be suited for a particular use or implementation.

The scope of the invention is to be defined by the following claims.

What is claimed is:
 1. A system for adaptive optical reference-freeconformal imaging vibrometry, comprising: a plurality of opticalelements arranged according to an arbitrary geometry of a structure orobject, configured to emit a single source beam to conform to thearbitrary geometry of the structure and substantially orthogonallyilluminate a surface at multiple locations to form a plurality ofsignals resulting from the scattered or transmitted light, each opticalsignal including information for measuring a surface displacement or avelocity or an acceleration at multiple measurement locations on thestructure; an optical receiver to collect said scattered or transmittedlight from said object through a distorted path; a scene-based wavefront sensor arranged in a closed-loop configuration to drive anadaptive optical tip-tilt compensator and a deformable optical elementto compensate for path distortions; a 2-d optical video receiver todetect a compensated image of the object under evaluation; amulti-channel optical interferometer to coherently detect surfacevibrations of said object under evaluation; a multi-channel receiverconfigured to receive the plurality of optical signals from saidmulti-channel interferometer and to generate a plurality of analogsignals; a multi-channel converter for adapting the plurality of saidanalog signals into a plurality of digital signals; a multi-channelprocessor configured to process the plurality of said digital signals todetermine the surface displacement or the surface velocity or thesurface acceleration of at multiple locations on said object and toreconstruct said compensated images to display the real-time structuraldynamics in real-time based on the surface displacements or the surfacevelocities or the surface accelerations; a diffraction-limited laseremitter directed in a substantially reverse-propagating direction withrespect to said received scattered or transmitted light by said object;a first spatial light modulator to encode inverted wave frontinformation onto said laser emitter beam; a second spatial lightmodulator to encode compensated image information onto said laseremitter beam; and an optical transmitter to direct said emitter beam ina substantially reverse direction with respect to said receivedscattered light.
 2. The system of claim 1, wherein said optical sourceis a laser.
 3. The system of claim 1, wherein said optical source is anincoherent source.
 4. The system of claim 1, wherein said object isreflective.
 5. The system of claim 1, wherein said object istransparent.
 6. The system of claim 1, wherein said object istranslucent.
 7. The system of claim 1, wherein said deformable opticalelement is a MEMS spatial light modulator.
 8. The system of claim 1,wherein said spatial light modulators (SLMs) are MEMS-based SLMs.
 9. Thesystem of claim 1, wherein said optical receiver is a Zernikeinterferometer.
 10. The system of claim 1, wherein said optical receiveremploys 2-d direct detection to demodulate said compensated object beam.11. The system of claim 1, wherein said optical receiver employs 2-dcoherent heterodyne detection to demodulate said compensated object beamas a function of location and time across the surface of said object.12. The system of claim 1, wherein said optical receiver employs 2-dcoherent homodyne detection to demodulate said compensated object beamas a function of location and time across the surface of object.
 13. Thesystem of claim 1, wherein a Zernike phase contrast microscope isemployed immediately upstream of said 2-d direct detector.
 14. Thesystem of claim 1, wherein a Zernike phase contrast microscope isemployed immediately upstream of said 2-d coherent detector.
 15. Amethod for adaptive optical conformal imaging vibrometry, comprising:substantially orthogonally illuminating an object; receiving saidilluminated light from said object; establishing a two-waycommunications link between said object and an optical transceiverthrough path distortions; generating an inverted wave front of saidreceived light using a scene-based wave front sensor in a closed-loopadaptive optics configuration; compensating for said path distortionsencountered by said object using said inverted wave front; generating acompensated image of said object; detecting 2-d video information ofsaid compensated image using direct detection; generating said directdetected video signal of said compensated image; generating a laser beampossessing a diffraction-limited planar wave front; generating a localoscillator beam using said laser beam; detecting said 2-d videoinformation of said compensated image using coherent detection with saidlocal oscillator; generating a 2-d coherently detected video signal ofsaid compensated image; executing a multi-point measurement of dynamicmotions of said object to reveal said object’s displacement, velocity oracceleration as a function of location and time across said object,using said 2-d coherently detected video signal; analyzing saidmulti-point measurement using a multi-channel channelizer with imageprocessing algorithms as known in the art; comparing said directdetected video signal against said coherent detected signal using saidmulti-channel analyzer with conventional image processing and algorithmtechniques to obtain a vibrational signal across the surface of saidobject as a function of location and time; encoding said wave frontinverted phase front information onto said laser beam by a first spatiallight modulator and tip-tilt compensator; further encoding saidcompensated image information onto said laser beam by a second spatiallight modulator; transmitting said encoded laser beam in a substantiallyreverse direction relative to said received light; propagating saidencoded laser beam through said distortion in a substantially reversedirection relative to said received light; transmitting said encodedbeam back to said object location, thereby completing the communicationslink and illuminating the whole-body of said object with a single beam;illuminating said object with said compensated image; and repeating anditerating said vibrometer process with illuminated object.
 16. Themethod of claim 15, wherein said optical transceiver is an opticalvibrometer with a laser source.
 17. The method of claim 15 wherein saidcoherently detected video signal involves heterodyne detection.
 18. Themethod of claim 15 wherein said coherently detected video signalinvolves homodyne detection.
 19. The method of claim 15, wherein saidspatial light modulators are MEMS devices.
 20. The method of claim 15,wherein a Zernike phase contrast interferometer, with a 90° phaseshifting feature, is employed immediately upstream of said 2-d directvideo detector.
 21. The method of claim 15, wherein a Zernike phasecontrast interferometer, with a 90° phase shifting feature, is employedimmediately upstream of said 2-d video coherent detector.
 22. The methodof claim 20, wherein said 90° Zernike phase shifting feature possesses acontrollable diameter, wherein said diameter is controlled to maximizethe phase contrast output of said Zernike phase contrast interferometer.23. The method of claim 21, wherein said 90° Zernike phase shiftingfeature possesses a controllable diameter, wherein said diameter iscontrolled to maximize the phase contrast output of said Zernike phasecontrast interferometer.